I really want to emphasize that no one should ever underestimate the use of buffs in this game because I have seen first hand that they can be some serious tide turners.
Soldiers:
Armor Piercing Ammo:
This is a must have. It would be irresponsible of a soldier t go into a gun fight without this.
Kevlar Vest:
Also a must have. Simply put, imagine a heavy soldier with kevlar vest and upgraded health. Indisputably the best tank in the game. But that does not mean that kevlar vest is exclusively useful for heavies. It is useful for all body types.
Engineers:
Weapon buff:
I would assume people understand how useful this buff is. This buff should always be prioritized over land mines and turrets, specially seeing as how bad the turrets target enemies.
Kevlar Vest:
This is probably the main reason why I am writing this thread. i have noticed many online players do not use kevlar vest. I feel that is a big mistake. Moreover, I think the number one priority of any and every engineer should be to buff medics with kevlar vests. Yes, KV (kevlar vest) to medic should be of higher priority than WB (weapon buff) to any other player.
Medics:
Improved life buff:
An extremely important buff. Although, I personally feel that this buff should not be handed out all willy nilly. Reason being, i think resurrection is much more important than health buff. Even still, i think it should be a priority to medics to self buffs themselves in order to keep themselves alive. A dead medic cannot rez other people...
Adrenaline boost:
Hardly a buff, but i will still discuss it. Not a useless skill, but requires way too much coordination to work. Give buff to an ally and use him as a decoy to drive enemy fire away. Although potentially useful, it is everyones choice if it is worth the supplies.
Metabolism:
Quite possibly the most useless buff in all the game. It really isnt useless, but it definitely should not be used when instead you can use it for resurrecting an ally or buffing someone.
Speed Buff:
Personally, i think this buff is also quite counter productive. Obviously, there are plenty of situations where speed buff is useful. The problem with this skill is that it is not permanent. Why waste a full pip on 5 seconds longer speed when you have other skills that are permanent.
Operative:
They have no buffs. How lame. They should have the medics speed buff. Have it self administrate and permanent.