Use this to sneak up behind enemies and quickly dispatch of them. The Advanced Targeting implant is invaluable for the infiltrator because it allows you to pick out wounded targets who you can kill more easily.
This is the fastest armor that has armor. Use it that way. This is what you spawn in so you'll always have it even when theres nothing else. Use the speed to strafe around, preferably with some sort of shotgun in hand, the slower suits and stay behind them.
This armor type is also fast but can be used for a much wider range of things other than strafing around opponents. This suit is hard to use especially as an infantrymen because it is fairly easy to kill.
This is the Infantrymens best choice of armor in an all out fight. Coupled with the personal shield implant it is quite formidable. The downside is it moves slower than the other non-mechanized suits, it still is best for general infantry combat.
Mechanized Armor Exosuit (MAX)
This armors strength is its ability to take damge and to have much bigger guns on it. Unfortunately 3 well placed shots with a decimator and its toast. the key here is to use the MAX suit for what it is intended for. Such as the AA MAX's(Sparrow, Burster, and Starfire) for shooting down aircraft and the AV maxes for vehicles and AI maxs for Infantry. Don't try to be Rambo in this, even though it feels like a walking tank, it is easy to take these down.