Engineers and Medics probably. Infiltrators and Light Assaults got their uses, but ren't needed in big numbers. You need only 1-2 infiltrators to cover the entire area in recon shizzle and you only need 1 or more Light assault to get spawn beacons on fun locations. Engineers are always handy as they usually are the ones in vehicles. They also repair MAX units, got turrets and can lay down mines. Medics are also needed quite much to keep everyone alive. You usually need more than 1 of those in case one dies. I'd say medics, engineers get a close second.
One infil with maxed out motion sensor and to hack terminals, one engi to drop ammo, two or three medics with nade bandoliers + rez nades and everyone else HA. So since there are more HA then anything else I'd say HA wins but every class has its purpose!
Medics... especially when people realize they can get oodles of xp by creating zombie armies with their magic grenades.
That's why you have HA's...... And Medics still have C4 (though primarily use mine for MAXes) You NEED an engineer for ammo. Otherwise all those medic revives are gonna wind up with everyone dry. If you go with 3+ MAXes for a crash, you'll likely want 1-2 extras to keep repairs up. Then you NEED minimum 2 medics, preferably 3 or 4. Redundancy to protect against wipes. You most likely really really really want a single infiltrator (and he BETTER have a scout rifle/SMG) A MAX or 3 can give your squad some good damage soak. An LA or 2 can be used for flanking to help punch holes. Not necessary but come in handy HA for the rest as frontline combat troops. Should be the first to die ALL classes are important to proper squad/platoon play. LA is the least "required" class but it still comes in handy to have a couple in your squad/few in your platoon to break stalemates.
Loaded question, No ammo you get to run back to the sundy or terminal. No rez or heal you get respawn. Infil helps tons with tracking and ambush. Those are my three support classes.
MAX is the class everything revolves around in serious competitive play. Then you want a handful of support players, with the remainder being HA and maybe a few token LAs. So HA are actually towards the tail end of things. In unorganized play (most public play, whether or not the rabble are in a platoon) the class mix is significantly different and even the best classes change (in part because the class mix is significantly different, which makes snipers and SMG infils and LAs much more viable than they are at higher end play.) This varies a little by base of course, but there's a reason everyone's MAX K/D tends to be doubled compared with their next-best class.
Definitely medic. Doesn't matter what kind of squad you're running, 1 medic will resurrect em all in a pinch or keep them in top shape in a firefight. An effective strategy is medic balling. You don't hear that about engineers, LA's, infils, or even heavy assaults. Of course max crashes happen, but maxes aren't really a class as much as a vehicle on legs. Plus you need an engineer in your team to play as a max (at least I do), basically a medic for max x-D
I going to go with engineer, always keeps me busy. sometimes medic or HA, all kinda depends whats going on.
There isnt one class (including heavy) that effects the squad most. This game is about balancing your squad. My personal preferance would be the "rangers" setup we use in our outfit. 3x Medic 2x Engineer 1x Infiltrator 6x Heavy (if there is really one person who wants to play light assault i may let them depending what we are doing). The medic is important to revive and heal, the engineer is important for ammo, the infiltrator gives battlefield recon and the heavy puts down the booms and pows. All are of equal import but only work well as part of a squad!
That one random guy who destroys the enemy sunderer had a bigger impact on the battle than your whole squad. If everyone plays to the greatest of their ability, their class won't matter as much. 5 Rambos are better than 20 Russian guys.
Hmm, non max / HA... I'd rank engie above medic, but only due to ammo. One engie on a scout / stealth flash sitting in a building with ammo down and repairs spamming is beyond useful, although repairing from flashes was nerfed right along with harasser rear seat repairs. After 1-3 engies or so, the usefulness declines unless there's a huge pile of maxes that need repairs, Medics scale better with numbers.
Neither my bow nor my LMG work as advertised, I demand a refund. I will admit that the 2nd gif is an accurate representation of hit detection, however.