TF2 Strategy Guide

Updates in Process
 
OVERVIEW
 
The jury is in, and it is generally agreed that TF2 is either the strongest teams, or at least one of them, in 1.4.2.  TF2 is a lot of fun to play as well, with a wealth of deap strategic possibilities.   
 
TF2 has the most numerous, flexible and varied offensive units, which when they are working together smoothly, create massive problems for your adversary.  Although lacking traditional scrolls, with weapon upgrades that cost only an action point ("AP") (i.e. a move) via the engineer, and the possibility of linking to a medic for a 50% stacking damage boost (or two medics for a 125% boost in damage) their high end damage, when you can set it up just so, can be staggering.  The possibility of medic-linking an upgraded demoman gives TF2 scary AOE.  Jarate is a powerful tool for assinating or hobbling two of your enemies most powerful and upgraded units.  Although lacking a ranged stomp, TF2's team bonus -- the ability to stomp without consuming an action point -- more or less gives every unit the ability to stomp at range 2 (4 for the scout).  In short, their offensive firepower is without equal. 
 
TF2 has weaknesses as well.  With only two healers, TF2 is very vulnerable to bad luck getting healers via the deck, and vulnerable to assination of healers.  Like other teams, and maybe more so, they can sometimes get the wrong combinations of units and items at the beginning of a game, and not achieve the kind of synergies they normally get from their varied offense.  They have no resistances of any kind except for a 10% magic resist on the healers, and only the Heavy has high health, making any individual TF2 unit except the Heavy and Spy quite squishy and vulnerable.  Even the Heavy and Spy are much more vulnerable than the key units of other teams -- an enemy that wants one bad enough will get it.  Their healing is among the weakest in the game (if you factor in the fact they only have two healers) and, with units with no resistances, they can have trouble keeping up, especially with AOE damage. 
 
TF2 has more units than any other team -- TF2 gets 18 (2 of each of the 9 types, scout, engineer, soldier, spy, heavy, demoman, flame thrower, sniper, healer) whereas Council, Dwarves, DE and Shaolin get 13 and Tribe gets 14.  Moreover, with the respawn tokens, TF2 can potentially deploy up to 20 total units in a game. The numerical difference is very real even after you account for the limited or situational offensive value of certain TF2 units (primarily healer, scout, engineer) as all other teams also have units of limited/situational offensive value as well.  However, TF2 has no armor and no super-unit, and no single TF2 unit can approach the devastating power coupled with solid defense that the best units of other teams can have.  TF2 can occassionally meet or exceed the offensive power of other team's best units, but cant match the toughness of other team's upgraded units.
 
TF2's wealth of offense means that no single unit is indispensible, and that it can be hard for an opponent to figure out what is worth using a special item such as a scroll to kill.  This is fortunate for TF2, because TF2 has great difficulty protecting units that an opponent is determined to kill. 
 
With no gear and almost no resists, TF2's defense comes mostly from its varied and consistent offense.  With the ability to create multiple simultaneous threats and the lack of a single ultra-high value target to focus on via a scroll or Drill, it can be hard to know how to attack TF2. 
 
TF2 is designed as a unit killing team, and they are perhaps the best team at winning by eliminating all enemy units.  With their numbers, they can  win a trading war provided they can deal with the enemies high value targets (such as tripple upgraded enemy units).   Because they are not particularly good at holding boost tiles, evicting units from boost tiles and lack special items such as drills or fireballs that can do substantial damage to crystals, they are not a crystal kill team per se.  Nonetheless, their powerful offense makes crystal kills a possibility.
 
STRENGTHS
 
1.  Numerosity:  Experienced players know that upgraded/powerful units are worth much more than garden variety units, but you dont need to be a rocket scientist to understand that more guys is still better than fewer guys.  With numerosity, straight up trades of unupgraded units are often favorable. 
 
2.  Varied Offense:  TF2's units do so many different things that the TF2 player can pose incredible problems for the opponent with clever deployments of varied forces.  With so many options, the TF2 has as much opportunity to be clever as any team, perhaps more. 
 
3.  No One Is Indispensable:   With so many units and so many offensive options, no one is indispensable, giving you great freedom to trade and threaten trades.  Well, you arent going to trade off a medic, but with that exception, you would normally trade literally any of your units for a runemetal'd enemy unit and quite often for an armored enemy unit.  Moreover, garden variety trades of unupgraded units can also be favorable (although thought is required).
 
4.  High End Power:  Upgraded and medic linked units give TF2 a high end kill power that, at times, can rival or even exceed a scroll.  A medic boosted demoman can do frightening damage to crystals and via AOE, and a medic boosted upgraded soldier or pyro can 2 or 3 shot most enemies.  A double medic boosted demoman is particularly frightening, doing 585 direct damage -- and nearly 300 AOE damage -- with every hit. 
 
5.  Skilled Assassins:  With jarate, spies, and high damage, tradeable units, TF2 has a variety of ways to potentially deal with hard/high value targets.
 
6.  Team Bonus > Limited Ranged Stomps:  Dwarves have no ranged stomp, Council have up to 2, and other teams have a limited number of units that can stomp at range.  Because TF2 can stomp for free, they can retreat, giving them the near equivalent of a ranged stomp with any unit.  Of course, they can also stomp and stay and attack again when that is preferable.  All in all, free stomps is one of and maybe the best team bonuses. 
 
WEAKNESSES
 
1.  2 Healers:  TF2's most serious weakness is also its most obvious -- TF2 only has 2 healers.  If they are buried in the deck, it can be a real problem.  With no resists, TF2 doesnt typically want huge numbers of units out (because of the risk of AOE), so even if you manage to get to the healer, you may be undesirably cluttered.  But the most serious problem is that it makes enormous sense for your opponent to pay a high price to kill a healer, it can put you in a bad spot if they manage it, and it can stress you to avoid the various risks to your healers.  TF2 can sometimes function tolerably with 1 healer, and other teams shouldnt mindlessly pay any price to kill a TF2 healer, especially later in the game . . . but at the very least, TF2's opponents have to give serious consideration to pulling the trigger if they have the chance. 
 
2.  No True Hard Targets:  Sure, the spy and the heavy are not always easy to kill.  But neither really compares to a geared Knight, high health geared Voidmonk, or bubbled geared pally (or any Dwarven unit) at holding a boost tile. 
 
3.  Set-Up and Deck Requirmeents:  Although not usually a big deal, TF2 is often not as quick out the gate as some other teams -- Tribe for example.  Much like the Dwarves, TF2 often requires some set-up time and particular units to operate at full power.  By this I dont just mean getting a healer -- rather, depending on faction and conditions, engineers and spies can be important for obvious reasons.  For example, against Council that deploys a geared archer early, its very nice to have an early spy.  But its more than just that -- depending on how things play out, you may want a particular offensive unit, and get something else.  For example, demomen are often the team MVP for TF2 . . . but getting one early as your only offense when the enemy doesnt have many units out is sometimes not optimal.   Moreover, TF2's sheer number of units means non-ideal combos will come up with some regularity -- for example, getting all your scouts, engineers, healers and snipers first may end up being just as challenging as having your healers buried. 
 
4.  Vulnerability to AOE/Clutter:  With only the healer having resistance, and the healer having a base heal of 400 at range 2, AOE can sometimes be a problem to keep up with.  Upgrading healers can help, and of course, with your powerful offense, you might be able to counter rather than heal, but its still often an issue.  Because TF2 has so many units, but you need or at least want certain ones (healer, often engineer, spy, etc) clutter, which increases the vulnerability to AOE, can be a problem.   
 
5.  High End AOE Requires More Set-Up:  Demomen are a very good AOE unit.  But a grenadier or wizard with runemetal is a threat to scroll attack at any point -- something one always has to be on guard against.  Its true that an upgraded medic boosted demoman will actually put out slighly more damage than a scrolled grenadier if he starts in range and boosted, and a double-medic boosted unit is truly fightening.  However, its a lot harder to set-up than a simple scroll attack.   
 
6.  Lack of Items That Can Be Used for Crystal Kill:  With high damage units, TF2 is a good crystal killing team.  But the lack of items does matter.  A single fireball, backed by boost tiles, can do massive crystal damage on the maps where fireballs simultaneously hit two crystals.  The Drill, on a debuffed crystal backed by boost tiles, also does huge damage. 
 
UNITS
 
Note on "Best" TF2 Unit:  Its not an academic forum topic, as the TF2 opponent has to know what unit is worth scroll killing, and TF2 has to decide what unit is worth a respawn token.  In general, the optimal TF2 unit to kill will most commonly be the medic, and its a good idea to save at least one respawn token for a medic.  However, there are times when a medic may not be the highest value target on the board (for example, in many endgames, when your opponent still has two medics) and also times when a medic is not reachable.  Beyond this relatively simple answer, things get more complicated as certain units are more valuable in certain situations or against certain factions.  For example, the spy tends to have a somewhat greater value when playing against Council, in light of Council's traditional reliance on the powerful archer, and somewhat less value when playing against the Dark Elves (mostly because Void Monks are a big part of their offense) -- but these are general observations only, and if your Council opponent has geared all his Wizards, you may value the spy less.  All of that said, player preferences tend to break down in three areas:  
 
(a) Spy:  The massive damage via backstab greatly limits your opponents deployments.  Without question a very valuable unit, but my personal belief is the Spy is still a situational unit, and there are situations where he is clearly not your MVP and shouldnt be respawned -- for example, in a TF2 v TF2 match where your opponent has 2 pyros out and no snipers deployed.  Or where Council has only Wizards out/geared and no archers/no geared archers. 
 
(b) Heavy:  Heavy is a little situational offensively as well, requiring the right situations to truly shine, but has the virtue of being potentially devastating and somewhat harder to kill than other TF2 units.  Many save their scrolls to kill Heavies.  Not to beat a broken record, but I feel that you have to look deaper, as depending on the situation, other TF2 units may be more threatening.  This is particularly true for the Tribe, which after 1.4.2 can now 3 shot a heavy with a garden variety axethrower. 
 
(c) Demoman:  As TF2's most flexible and easiest to use AOE unit -- one that can devastate when upgraded and with the medic link --  the Demoman is often my MVP.  I am very, very concerned about deploying/losing Demomen early, because you never know when AOE will be needed.  This is particularly true on maps which encourage clutter (such as the Tribe map) or against teams that are more likely than average to have clutter issues (such as TF2 itself).   Even as to Demomen, I feel you have to analyze the situation, but I tend to place Demomen above the spy and heavy in the abstract. 
 
(d) Others:  Pyros and soldiers are great, but its relatively hard to make a case for them as the general MVP of the team in the abstract.  But Hero Academy is not played in the abstract, and if you are short on offense, using the respawn token on a soldier or pyro might make sense.  Similarly, if a forward pyro is causing bad threads, why not scroll kill him?  Because all of TF2's core offensive units are good, and their strength varies with the situation, you should feel free to make your call based on what the board actually looks like, not some abstract ranking of the units.  All of that said, I have never used a respawn token on an engineer, scout or sniper, and if it is situationally appropriate to do so, it would be in some extremely rare situation, such as an endgame with little else left.   
 
The factual information that follows is from Hamlet's awesome mechanics guide, with strategic information from me, with community input.
 
Spy (2):
650 HP
200 attack (P), range 1
If attacking a unit from behind, 400% damage.
Cannot be targeted for attack by a unit at range (except as a corpse), except a Pyro. Can be targeted by a unit in melee, by a Pyro, by a spell/item, or by enemy attacks that target corpses. Takes AoE damage normally if something else is the target.
Move 2
Analysis:  Can one shot an 800 health 0 resist unit from the back (backstab), and with an upgrade does 1040 per backstab, allowing one shotting of additional targets.  Nothing takes more than 2 backstabs from an upgraded spy, and only a few units can withstand 2 backstabs from unupgraded spies.  The massive damage via backstab greatly limits your opponents deployments.  Spies are excellent units, and deployed forward or sandviched spies can really tie your opponent in nots.  Of course, you dont really want to deploy a spy in the vicinity of an enemy pyro, or in a cluttered group of your own units (since the spy will get AOE'd), and need to be careful where you put him given his low health.  Moreover, the fact that spies are so useful, combined  with their low health, does limit their use somewhat.  If you are not going to be able to safely retreat, you probably want to stomp a unit with runemetal or a double upgraded unit and "merely" netting an unupgraded super unit or archer may actually be a close call (although I would probably make the trade, depending on the board).  Against a careful opponent, spies shouldnt get too many high value kills -- their value is more in restraining enemy choices and forcing the enemy to set up in a way that is helpful to you.  Specifically, spies work best in combination with other units, such as Demomen and Pyros as by forcing your opponents to group, spies set up the enemy for your AOE.  Thus, like most TF2 units, spies are awesome and yet a bit situational at the same time.  Spies are a potentially good candidate for the respawn token, subject to the specific situation your in.  Spies are a good candidate for a sandvich when the enemy units are so scattered it will really mess with them -- be careful they cant just reorganize and render the sandvich useless.
 
Scout (2):
650 HP
100 attack (P), range 1
When hit, jumps one square away from attacker (diagonal if attacker is knight’s move away). When the attacker has its own push/pull effect, the Scout behaves like any other unit. When hit by Chieftain, the Scout jumps back and is then pulled, usually winding up where he started.
No AP cost to deploy (and can be deployed at 0 AP).
Move 4
 
Analysis:  Scout's have at least 4 uses:  (1) because they deploy for free, they are used to cycle through your deck and help get to the important stuff; (2) grabbing a boost tile, when that matters; (3) screening a high value unit from direct attack by blocking the enemies line of sight/fire; and (4) as your ranged stomp, either diving in and out, or simply making the stomp as a suicide manuever, saving the need for a more valuable unit to do so.  All of these uses have potential value, and the Scout should not be sacrificed without thought.  Its a mistake to just throw it out there and assume that its not worth the opponent's time to kill -- this will sometimes be right if there is enough going on elsewhere, but if the situation permits, its well worth your opponent's time to grab a free scout, and you shouldnt allow it lightly.  Thus, while you can use a Scout to block line of sight to a more valuable unit, make sure you have a concrete reason for doing it and are not merely sacrificing the Scout.  In short, while it would be silly to use a respawn token on a Scout (although you could dream up an endgame situation where it would make sense), the Scout has real value and shouldnt be given away.  Dont be afraid to heal him when the situation permits without undue effort. 
 
Be careful about where you place him when the enemy has AOE like the grenadier.  It can stink when the Scout gets knocked back into postion to allow the grenadier to AOE a bunch of your other units.   
 
Soldier (2):
800 HP
300 attack (M), range 3
At range, knocks back target away from Soldier (diagonal if target is knight’s move away).
Move 2
 
Analysis:  With 300 base damage, the soldier is good trade fodder.  For this reason, I often deploy them early, for example chosing to deploy one before a demoman.  While the knockback is a bit limiting in their tradeability, there is no knock back if you attack from melee range.  While I would gladly trade a soldier for an archer, super-unit, or really any enemy offensive unit that is deployed in an annoying fashion, this does not mean that soldiers are without independent value.  Upgraded they make excellent units to jarate-kill something.  Upgraded and medic boosted, they are a big time threat to any unit that wont be knocked back, or will be knocked into range of another high damage unit (sniper, pyro, etc).  Thus, although they probably are the least valuable of TF2's core offensive units (a debateable point) in some abstract sense, they are routinely useful in a variety of ways.  While you probably dont want to use a respawn token on a soldier (unless your short on offense), and will often use them as trade fodder, dont throw em away -- they are part of your core offense and synergize well your other units.  For example, one common synergy is knocking a unit into the path of a sniper. 
 
Soldiers are not typically the best candidate for application of the sandvich buff, but there are exceptions.  If a soldier can jump into melee range against a high value target, it can generally make the kill and trade itself off, and there may be times when your enemy cant easily avoid this if you pre-sandvich.  
 
Sniper (2):
650 HP
100 attack (P), horizontally with unlimited range, or any direction in melee range
Kneels at end of turn, giving +250 damage (before resistance) to first shot of subsequent turn, unless Sniper takes damage or moves before shooting.
50% damage against crystals (applies to Assault bonus, but not to kneeling bonus).
Move 2
 
Analysis:  Even after the 1.4.2 nerf, snipers are still a big time threat to jar kill something, often with a scout flying in to do the stomp.  You may need an extra shot, and it may not work, but dont put a high value target on the same row as a sniper (or leave a jar unused) without thinking it through.  Snipers can sometimes create stomps in other ways -- for example, sometimes the soldier can knock an enemy unit into the sniper's row to facilitate a 3 hit KO.  Of course, 350 or 380 damage is quite annoying in and of itself if the enemy's healer isnt close.  At times, you might gamble that the enemy has no healer and unleash your crouched shot, knowing that at worst you'll probably get that AP back -- i.e. its not much of a gamble, and will often make sense.  For the same reason, the Snipers' crouched shot is a decent way to burn an "extra" AP you dont have much use for, as if the enemy doesnt heal the unit you hit, you may be able to stomp it. 
 
There are four logical choices for where to deploy a sniper: 
 
(1) the sword tile - on certain maps, a sniper on a sword tile makes a lot of sense, as 450 for the first hit, plus 200 follow-ups (more with upgrading), creates a lot of possibilities for stomps.  
 
(2) enemy's deployment row - this can be particularly annoying early, when the other side doesnt have a healer.  However, at times, its fairly easy for the enemy to deploy around this (for example, if they are TF2, they just whip out their spy) so think about whether it makes sense given your situation;
 
(3) in line with the enemy crystal:  An unupgraded crouched sniper does 350 crystal damage, or 500 if you have 1 boost tile.  That isnt bad, it adds up fast, but make sure that you are going to either go for crystal or at least threaten it before you spend the AP doing this.  Also consider that the crystal may be an AOE target, and that you sniper doesnt do crouching damage if hit with AOE the turn before.  Eventually, if you keep doing 350/500 hits, the other side may be forced to block the crystal, and if your ready for that it can be an opportunity to go after units;
 
(4) on any row with multiple exposed units that you can threaten a stomp of, or that cant be healed without reshuffling.  Sometimes its worth spending an AP to reset the sniper if the enemy will need to spend several AP dealing with it.
 
Be careful of putting the sniper somewhere that creates AOE problems.  An AOE hit breaks the crouch, so its pretty easy for a sniper placement to be counter-productive. 
 
Snipers are not candidates for the respawn token or sandvich.  They are very valuable units in a supporting role, but a bit situational -- kind of hard  to be sure you would get enough value on one to use a token in lieu of using it on one of your core offensive units.   
 
Medic (2):
800 HP
10% M resist
200 attack (M), range 2
Heals for 200% attack, revives for 50% attack, range 2
Self-heals for 50% of any healing done, not including overheal.
Link to full-health ally in range 2 to increase their attack by 50%. Link lasts until target and Medic are more than 3 apart, Medic links/heals/attacks a different target, Medic takes damage, or target is KO’d (it does not break if target takes damage or Medic heals target).
Two medics can link the same target, resulting in 225% normal damage.
Move 2
 
Analaysis:  If you factor in the fact that there are only 2 of them, TF2 arguably has the worst healing in the game, with the fact that their are only two perhaps trumping their healing advantages (upgradeability without using a limited runemetal, and self-heal).  Just getting one out of your deck can be a problem, and making sure the enemy doesnt take one out is often hard.  They should be protected, and its often a good idea to save a respawn token for one.  Its also generally a good idea for your enemy to burn a scroll, jar, drill w/e to take one out.  All of that said, with the respawn token, sandvich and self-heal that happens when you heal others, it is sometimes possible for TF2 to function tolerably with only one healer, if you can hide him in a group of units or behind crystal.  Accordingly, there is probably such a thing as paying to much to stomp a TF2 healer.  For example, Shaolin can double dragon + bamboo a healer on turn 2 if they have the stuff -- but whether it would be a good idea to pay so much is highly debateable. 
 
Despite being maybe the worst at healing of any healers (again considering that there are only 2) the Medic is clearly more valuable to TF2 than any other team's healers, with the possible exception of the Paladin (giving the Dwarves credit for having more of them).  This is the case because the medic link to a demoman, pyro or soldier can pump out tremendous damage.  Links to heavies are less commonly useful since you need to link up the turn before to do better damage than just adding an extra attack by the heavy.  In addition to considering whether to link the heavy for (additiional) use in a future turn, check to see if the heavy can kill something with a medic link and a jar that turn.  While unusual, links to spies or engineers can occassionally win games (especially in the endgame).  Medic links to snipers can occassionally be an annoyance to your adversary, but are a somewhat infrequent tactic given that the modest pay-off probably isnt worth going out of your way for. 
More categorically, the medic link has several uses:
(1) High end Shock and Awe Style AOE.  Demomen are good without the link, but lack the possibility that grenadiers have of leaving 3-5 units on the ground after a devastating scroll attack.  The medic link gives Demomen the possibility for this kind of damage.  Although somewhat harder to set up than a scroll attack, you can potentially do medic boosted attacks for several turns.  If you get the chance and your enemy is cluttered, a double medic boosted attack can easily win a game.   
 
(2) Hunting or Detering High Health/Armor/Resist Targets:
Boosting a soldier or pyro (usually upgraded) is about the only way to kill or keep high value targets away when your jars are gone, absent (sometimes) a spy.  Because you only have 2 jars, and spies can sometimes be manuevered around, you need the medic link combined with a high damage unit to kill or deter the highly dangerous armored targets.  Moreover, just because you jar something doesnt necessarily mean its easy to stomp it -- a medic link can be a big help, allowing you to one shot the jarred unit when otherwise might not be able too. 
 
(3)  Momentum:
The damage of linked units is so great, that if you can KO something that needs healing and/or in a position where your unit isnt at risk, you will often have played yourself into a spot where the enemy cant avoid you doing real devastating the following turn.  This is like sending a tank into a dug in platoon.  Sure, in the abstract they could kill the tank, but when you plant a shell in their midst while barelling forward at 60 mph, good luck to them. 
 
(4)  As a "Why Not" Move:  The medic link should sometimes be used as a "why not" move when its "free" -- i.e., you could KO something in 3 attacks without the link, or 2 attacks plus the link -- i.e. 3ap to KO either way.  Even if you have no real idea how to use that medic link in subsequent turns, you might as well link up just to give yourself more options in future turns and potentially deter some tactics you havent though of from your adversary.  Its a "free" move
 
Engineer (2):
800 HP
200 attack (P), range 2
Can permanently upgrade an ally’s attack power by 30%, range 2.
Move 2
 
There are lots of issues to think about with engineers, starting with where they go.  You dont know that you'll get your second one anytime soon, and you dont want crowding anyway, so in an ideal world you might want the engineer in the middle.  But sometimes that is a recipe to get AOE'd.  There are lots of options, and I dont know that there is a single best place -- just give it some thought.  The second issue is when to upgrade and what.  To some extent, this depends on the team your facing and the units that are deployed.  For example, if playing Tribe and your opponent doenst have Chieftains or shielded units out, do you really spend the time to upgrade the soldier?   It wont help kill anything currently on the board faster.  That said, if you have time, or cant think of something more productive to do with a single AP or two, its almost always (eventually) useful to get medics + all of your key offensive units upgraded -- just prioritize the ones likely to be actually useful in the immediate future, and dont sacrifice too much positioning to to do it.  Upgrading units without a specific reason on the board can also be a recipe for the other side getting entrenched positions on you -- so you really have to think about it, and shouldnt mechanically upgrade (or even deploy the engineer) right away.
 
Engineers are frequently still alive in the endgame, and it can make sense to spend an AP to upgrade them, at least at times, and eventually.  They can sometimes be effective trade fodder when you have two around, or when you already have your units upgraded.  Play TF2 enough and you'll probably win a game by medic-linking an upgraded engineer and killing something more important.  That said, in general aim for them to be a stationary vending machine and only vary when you see a good reason. 
 
Heavy (2):
1100 HP
100 attack (P), range 3
At range, cone attack deals 100% damage to main target and up to three nearby targets (see http://iam.yellingontheinternet.com/2012/08/10/hero-academy-mechanics-guide/#appendix).
In melee, 200% damage, no splash.
If consecutive actions in one turn are spent attacking, +50 attack power each shot, with Engineer/Medic bonuses applied first, but the melee bonus applied afterwards
Move 2
 
Analysis:  Although generally considered one of TF2's stronger units, the heavy is a little situational.  The heavy basically has 3 rolls:  (1) 1100 health blocker.  He is no Knight, but Heavy can provide a reasonable amount of protection/boost tile holding for times when the spy cannot (or to supplement the spy); (2) ranged AOE damage dealer.  Note that the heavies single target ranged damage is pretty uninspiring -- unupgraded, 5 ranged shots are required to KO a vanilla 800 0 resists unit.  Even upgraded, he takes 4 ranged shots to KO something.  So you want to be hitting multiple units/crystals, and its particularly nice if you can stand on a sword tile while doing it in which case the heavy does nice damage; (3) a melee unit that does heavy damage -- remember, the Heavy does x2 its normal damage in melee, and 3 shots from a non-upgraded heavy do 900 damage.  Upgraded, with the possibility of 4 shots or even jarate, the melee heavy can do some serious damage. 
 
Tip: damage continues to build as long as you dont stop attacking with the heavy -- you can switch from melee to ranged or back, as long as you dont stop attacking.  Also, stomping a unit on the deploy tile counts as an attack, not a move, so continues to build damage. 
 
Many folks will automatically scroll kill the Heavy or use a respawn token to bring it back.  This doesnt make sense.  You should do an analysis of which units are most threatening given the board set-up before scroll killing a heavy, and TF2 should likewise think about what a Heavy would actually do given the board before using a respawn token. 
 
Tip:  Heavies are definitely better on certain maps than others.  The teleport map, for example, because a heavy on the sword tile can sometimes hit 3 or even 4 enemy units clustered around the teleport and boost squares.  The map with the two crystals close in is also great, because the heavy can sometimes hit both crystals from range, and there is a sword tile in between the crystals which gives possibilities for massive crystal damage and/or damage to adjoining units.  The Shaolin map, with the speed tile and a sword tile, should also be lovely for heavies.   
 
Pyro (2):
800 HP
300 attack (M), range 2
If target in melee range, also hits square behind for 100%.
Move 2
 
Analysis:  Despite their great damage and potential to hit two enemies, Pyros 2 range and 2 move means that they are not necessarily easy to use effectively.   They are terrific offensive units *in combination with the team*, but dont win games with devastating solo moves as commonly as spies, heavies and demomen can.  Unless you can safely occupy a forward position, you'll often need clever positioning and multiple threats, to make them work.  That said, a sandviched upgraded pyro can sometimes cause great problems for your opponent, and is usually something to look at.  Pyros can benefit greatly from working somwhere near a deployed spy, as the spy forces units to stack up creating an opportunity for the pyro.  At times, Pyros benefit from a medic link, as the damage of a linked pyro is so high that the range and mobility issues may not matter -- at times, this can be a good way to kill those pesky highly armored, helmed, bubbled or high health units.  While using a pyro to jarate kill a +3 unit is not ideal if you will lose the pyro, this can sometimes be advisable. 
 
Pyros are fairly good at trading themselves for enemy units, and while you'll hope to bag an upgraded enemy unit or a 2 for 1, grabbing something like an unupgraded archer or super-unit will probably make sense as well, depending on the board.   
 
Pyros are terrific anti-spy units because they are the only unit that can hit spies at range, and can 2 shot a spy when upgraded.  Pyros thus have a higher value in TF2 v TF2 match-ups.  In fact, there can sometimes be a bit of a cat and mouse game, as in an ideal world, everything else being equal, you would hold your spies/pyros until seeing where the enemy deploys his spies/pyros.  When pyros have forward positions, spies can sometimes feel like a liability. 
 
Demoman (2):
800 HP
200 attack (M), range 3, ignores LOS
At range, 100% to target, AoE for 50%.
In melee, 100% to target, no AoE.
125% damage against crystal, if crystal is main target (including Assault bonus).
Move 2
 
Analysis:  You cant bubble them, or give them a shield and helm, they cant be used with a scroll, and you only get two, so they probably arent as good as the Dwarves Grenadiers in an abstract sense.  But with the ability to upgrade them to 260 for only an AP, and to medic link them for 390 damage (or 585 with two medics) the damage they can put out is potentially staggering and game winning.  At the same time, TF2 has so many threats that the opponent cant just give up a runemetal unit to get one, and if they have to give up a scroll and a quality offensive unit, that is usually a net gain (although a bittersweet one) as well. 
 
While one doesnt normally want to rank TF2's offensive units, there is no question that a Demoman is more commonly highly valuable than a soldier or pyro, and other things being equal, you dont want to trade off a demoman in the early game.  When you start with many offensive units, you might even chose to wait on deploying the grenadier until the board conditions are favorable for one.
 
As with a grenadier, a common mistake is nibbling with an unlinked unupgraded grenadier when its easy for your opponent to heal up in fewer AP than you used.  If your not careful, you get behind in development, and you have nothing to show for it except some crystal damage that may be totally irrelevant.  Nibbling *can* be appropriate, but you always need to think hard about whether you should be developing instead. 
 
Your primary goal with demomen should be to get them upgraded and positioned with medics so that you can AOE your opponents into a pulp.   But you cant really force it, and if the opponent isnt cluttered or the board doesnt lend itself to the tactic, you may want to do something else while keeping the demoman in mind for the future. 
 
With their nice range and lob, one doesnt typically think of sandviching the demoman and it will rarely be the best move.  However, there definitely are times when sandviching a demoman can win games against cluttered opponents, when you cant get in range easily otherwise, where you threaten to kill a medic or occupy a sword tile.  Of course, you need to make sure they cant thwart you with a simple reorganization.
 
With their high value, Demomen are good candidates for a respawn token in the early and particularly in the mid-game if you are facing a cluttered opponent or anticipate that they may become cluttered.  Additionally, if you are going for a crystal win, its often important to keep your demomen around to prevent turtles.   
 
Upgrades:
 
TF2 Doesnt have any shields or helms, and weapon upgrades come only via the engineer. 
 
Jarate (2): Targets one enemy unit. -175% to both resists for one attack.
 
Analysis:  While Tf2 can kill high defense/ health units without jarate, it requires proper set-up which you may not be able to manage under pressure.  Jarate is, in an ideal world, akin to an insta-kill spell, allowing you to take out any enemy unit with easy.  Of course, it doesnt really work that way in practice, Jarated units dont kill themselves, you need to PLAN for how you will actually perform the execution.  At times, even if you dont have a kill right away, jarate can force a retreat, and that can give you important breathing room.  However, many times a jarated unit can still function effectively -- particularly something with range 3, and/or something that can be bubbled.  Moreover, since AOE damage will use up the buff, the jarated unit can even "protect" other units/crystal from AOE, since you wont want to waste the jarate buff.  Accordingly, "painting" a unit that you cant actually kill right away is something to think twice about -- it *might* be good, especially in certain end-games, but just consider the risks.   
 
So how do you perform the execution?  There are many ways.  The classic crouched sniper is obvious (just plan for the stomp), and its equally obvious that soldiers and pyros, particularly when upgraded can often do the job (although it may be a trade if you dont have a scout in range to stomp, buying you time to retreat the attacker).  Less obvious is the fact that upgraded Heavies in melee range can sometimes be your killer.  You also have to remember to check for medic links that might allow a kill. 
 
What to jar is just as tricky a question; after all, you only get two.  My rule of thumb is pretty simple -- any +3 enemy unit (ie. helm, shield and runemetal) that is or is likely to be a PITA and cant be dealt with some other way.  Sometimes, when a enemy unit that isnt a +3 is causing nightmarish problems, you have to jar it -- but that is an unhappy lesser of two evils thing only, and not something you want to do. 
 
Against TF2, you can jar a bit more freely since all of the core offensive units have decent value, but make sure you are using it for something that really matters - i.e. not just getting a free soldier when your enemy has plenty of offense out.  If you pull the trigger too lightly, you may miss out on the opportunity to jar-kill a medic, or to remove a deap heavy that cant be taken out some other way.  I see many automatically jar-kill a heavy when they can.  While I am a little skeptical of doing it automatically, it can be logical, at least if the heavy is annoying or threatening to be.  Those that autokill the heavy are likely thinking that the heavy is generally the hardest offensive unit to take out, but while that may be true, heavies arent always the most threatening unit -- you might, for example, regret not having that jar when your opponent has a medic linked Demoman in the mid-field.  Jar-killing a medic is probably the highest value use of the jar in the abstract.  That said, do think about the board and position -- there have been times when I could have done so, and havent pulled the trigger given the rest of the board. 
 
Sandvich (2)
Targets one friendly unit. 500 heal
+2 move for unit’s next move (buff no longer falls off if the unit is moved by any effect and survives KO if unit is healed).
 
With proper and creative sandvich use, you can almost always get something tangible for your sandvich, be it a kill of a unit without losing one of your own, a safe retreat of a unit you are trying to save, or just forcing your opponent into a major reorganization (for example with a sandvich'd spy) that you can exploit.  Using a sandvich and not getting a tangible benefit is no different than losing one of your offensive units for nothing -- its bad.  I tend to value a sandvich as about equal to an unupgraded enemy offensive unit in a good position, or a friendly TF2 offensive unit that is likely to be useful.
 
Sandvich's have three uses. 
 
(1)  Healing:  dont use it for a garden variety heal -- make sure you are saving a useful unit that you couldnt otherwise save.  
 
(2)  Pre-Applying for the Movement Buff:  this really lets you be creating and cause problems for your adversary.  A pre-sandviched upgraded Pyro can often bag free unit(s).  A pre-sandviched Spy can force a major reorganization of your opponent's forces, leaving them vulnerable to demomen or pyros.  Heavies can often work too -- dont forget, the heavy is deadly from melee range, and the sandvich can get you there with time to kill and retreat.  Soldiers are less common choices, but be sure to at least think about it -- it can work, because a soldier that can jump in melee can be deadly.  With their 3 range, Demomen are not common choices per se, but dont neglect to think about it -- on crowded boards, the ability to get a demoman to the front lines can be deadly, and might otherwise be lacking.  Moreover, you can sometimes directly target the medic that way rather than a crystal -- for example, if they are on the sword tile on the Tribe map.   
 
(3) To jump over two or three units:  Generally speaking, there isnt any gain to applying (eating?) a sandvich on the same turn you want to move, as it costs an AP to do it, and you could just move the attacker twice.  The exception is when the sandvich allows you to jump over 2 or 3 units, and you could not get to that square by moving your unit twice.  This can be handy for spies, and sometimes for other units as well -- for example, Heavies that want to get into melee range for the double damage buff, or any unit that wants to get into the sword tile. 

Respawn Token(2):
Targets one KO’d friendly unit. Unit is returned to hand (ugprades are reset). No AP cost (and can be used at 0 AP).
 
Dont use these pups on garden variety offensive units unless you are starved for offense.  Rather, you want to save one for an offensive unit likely to be particularly helpful given the board situation, such as a demoman if your opponent is cluttered, a spy if your opponent has runemetal archers out, or anything that makes sense to you based on the specific situation.  The "why" isnt really too important, as long as you have a reason other than "well my unit is dead".  Most of your core offensive units can meet this standard some or most of the time, but soldiers rarely will, and the only time I use a token on a soldier is when I'm short on offense.  Additionally, most folks like to save at least one token for a medic -- at least till the game advances sufficiently that you feel comfortable that you wont likely need one for that. 
 
It can be tempting to use a respawn token just because you have two of them cluttering up your hand, but if you plenty of offense out, using a token just to save a random offensive unit (such as a soldier) isnt necessarily a great use.  
 
 
General TF2 Strategy
 
The best defense is your offense.  Getting a diversified team out there that creates multiple threats on offense, and makes it hard for your opponent to penetrate deap with a high value unit is important.  Engineer upgrades of your core offensive units are important to achieve this, although somewhat less so in a TF2 v. TF2 mirror match.  It is often particularly important to deploy, upgrade and medic link your demomen when your opponent is cluttered or may become cluttered, but done too early, your demoman may be biting on air.  On the teleport and movement boost map, watch the sword tiles closely, and look for chances to get a Demoman or Heavy planted onto one. 
 
While TF2 can win via a crystal kill, going into a match thinking that will be your approach is usually a mistake, as TF2 doesnt necessarily do well without a diversified offense out to provide multiple threats.  In other words, you should generally set-up and see what happens. 
 
While there are times when early aggression is appopriate of course, be cautious about spending a ton of AP just to do a little crystal damage and some unit damage that can be healed in an AP or two.  For instant, the early attack with a demoman on a crystal with 3 ap, plus 1 to go and 1 to retreat, will often be a mistake (especially) without a boost tile.  The other side whips out the healer, heals the offensive unit that was splashed once, and uses the time to complete their deployment.  If you dont end up seriously pursuing or threatening a crystal win, you may have wasted time for nothing. 
 
Because TF2 has so many offensive options its tough to give much more specific guidance.  More so than any other team, your manuevering and set-up is chess like and deap -- where you put what when matters a great deal, and its very common to see a hidden better deployment the more time you spend looking at a position. 
 
FACTION SPECIFIC GUIDANCE
 
Against Council:  This is a generally favorable match-up, but there is plenty of room for strategy.  One the one hand, Spies are terrific at shutting down archer.  On the other, Wizards can more effective than usual because TF2 has no innate resists, and TF2's healers have no special advantages at healing (other than their self-heal).  Moreover, with only 2 healers, you have to keep them safe, meaning that it can be quite a challenge to heal everyone without being exposed.  In addition to the advantage of spies, TF2 has so many high damage units that Council's +3 units are hard to keep safe -- especially if jarate is still in play.  Council may want to spread the upgrades around -- but with TF2 having so many high damagers, this is of uncertain effect.  Moreover, while Knights are good blockers, demomen can be a problem.