I figure, I'd make a thread like this to help people play the classes to the best of their abilities. Feel free to post your own guides and help tweak mine so that we can help each other Mann Up and beat the piss out of Robots. I'm going to start with engy, because I feel that I'm the best out of all classes at that.
Engineer
Primary -
Frontier Justice - I find this to be the most useful of the shotguns (close second being the Pomson). This is due to you being able to store tons of crits away and you will often max out at 35. Rarely will you want to or need to use your shotgun, but if the need arises, crits are very useful.
Secondary -
Wrangler - There is no need to have anything else, even if you don't use it at all. The Wrangler is helpful but engineers rely on it a bit too much I feel. The large damage reduction is a plus when you are facing up against giants but you mostly want the turret on auto-pilot. The reason why I dont feel you should use a lot is because it requires you to expose yourself to aim properly, which the robots catch on quick to take you out.
Melee -
The Jag - Just because you won't melee anything mostly ever. The extra build speed is always a plus. For the love of god don't be stupid and use the gunslinger.
UPGRADES
Sentry Attack Speed- Max it out but spread the upgrades out evenly as the difficulty increases. This should be your first purchase.
Building Health- Again, this is a standard one that should be spread out as the difficulty increases. I would say to start upgrading this one after you have one point in metal capacity and melee attack speed.
Metal Capacity- You can either max this out or leave it at 3 points, depending on the money you have available. You will definitely want at least 3 points in this.
Two Way Teleporter- This is useful, however I would wait until round 2 or 3 to upgrade it (assuming you're not playing endurance)
Melee Attack Speed- This follows the same rules as metal capacity - however I strongly recommend a fourth point in it. Most engineers overlook the melee attack speed, but it is essential for hammering your sentry through intense fire.
Dispenser Range(Optional) - This is helpful if you have extra cash to drop. Putting your dispenser farther away from the turret increases its likelihood to survive and can also help the group keep optimal positioning instead of having to run to the dispenser to refill ammo.
(I feel as though I'm missing something else - Will Edit Later)
If you have any extra cash left over (don't forget to save some for canteens), feel free to upgrade bullet resistance, then blast resistance. If your team is doing things right, blast resistance will be unnecessary. It is useless against the giant soldiers/demomen, since they will melt your face with or without it. Bullet resistance is always helpful if you have the cash, but since you're hiding behind your sentry, it will shield you from some damage. The additional mini sentry is a piss poor upgrade. I don't recommend it.
CANTEENS
There are three canteens for you to consider. Each has it's own time and place, so don't think you have to stick to one for each round. Or even for an entire round for that matter. Don't forget you can buy canteen powerups (and upgrades) during the round.
Uber - This canteen will make you and your turret invincible for a time. This is one of those oh shit buttons when you have a giant heavy/rapid fire soldier on your ass. You can't outfix them if they continue to pummel your turret even with max swing speed. Charged soldiers usually can be healed through, so consider using this in rounds where you think you will be under heavy fire.
Crit - This canteen will triple your sentry's fire speed. Use this when DPS is an absolute must (such as tank levels)
Instant Buildings - This one automatically upgrades all of your buildings to level 3. If you feel your turrets are getting destroyed a lot, you may want to pick this one up. I usually grab this from the shop if the wave is going to hell and need it.
STRATEGIES
- Much like in normal play, you will want to set up somewhere guarded. Don't be afraid to move the turret around, as it will place much faster than in normal play.
- Keep your dispenser handy. Most teams will want you to place it near the heavy. This isn't exactly wrong, but at the same time, your sentry is about as important as that heavy. If there is a ammo box/health pack combo nearby, you may consider moving the dispenser elsewhere. Try to find a compromise. Maybe ask the heavy to move to you if necessary.
- Learn to dupe the sentry busters. If you're the only engineer, this one's easy. Sometimes it's hard to tell where the sentry buster is going with multiple engineers but keep an eye on it. Learn the paths it will take. Once you have realized it has locked onto you, pick up your sentry and run towards it (if safe to do so). This will cause it to stop and detonate. However, it will also cause another one to spawn very shortly after, so make sure your team helps you out and destroys them when they can. Make sure you intercept it in a safe area.
- When auto-firing, sentries will go after the smallest threat first. What I mean by this is that they will attack hordes first, then giants, then tanks.
- Know when to wrangle. If you are in a spot with a piss poor view that requires you to expose yourself, just pick up the sentry and hide it. Don't try to protect it with the wrangler if you can easily die in the process. Use it at longer ranges (obvious for anyone who has ever played engineer). I prefer to leave it auto-fire 90% of the time mainly cause I'm mostly concerned about the turret surviving.
- Keep an eye out for spies and snipers. These two can devastate the front lines, but are easy to spot and take down. If you have nothing going on at your sentry, wander off a bit and scout out the area and take down any of these that you can. Don't wander off too far though.
- Upgrade during the round. You will know where your teleporter is and most likely be nearby it. If you have a moment, zap back to the shop and get essential upgrades. Since you're mostly stationary, you'll have more freedom to prepare for the next assault in your protection zone.
- Do not, I repeat, DO NOT leave your sentry in the back by the bomb site. This is a useless point unless the bomb is right there and there are enemies coming for it. If you need to, pick up your sentry and teleport back to base, THEN place it. Pay attention to where the bomb is at all times and set up accordingly.
Expect upcoming tweaks, added suggestions, and revisions. I did this at work, so I know it's not gonna be perfect, but I wanted something to do...other than work...