Well let's see
Engineer:Good for taking out vehicles, has a sub machine gun or a carbine. Best at short range, Burst at medium range, struggles at long range. non-guided RPG. Good for light and heavy vehicle, low splash damage, struggles to kill infantry. Good for taking out walls and cover. Guided RPG good for taking out vehicles but cannot take out infrantry
Assault:Good for healing and reviving, has an assault rifle. Spray at short, best at medium where you burst fire, decent at long range while singe shooting. Unlimited medkits which makes for faster healing for you and your teammates. Reviving for your team will give you more support because everyone knows 2>1. Or you can switch your defibs for a grenade launcher. Grenade launcher:Medium splash damage, average damage, good against light vehicles, suffers at heavy vehicles. Able to take out walls and cover.
Support:Good for giving your team ammo. Heavy Light Machine Guns(LMGs for short) Spray at close range, burst on medium(Though suggested to have a bipod to limit recoil allowing you to go full auto without the recoil destroying the guns effectiveness), suffers at longer ranges. Unlimited ammo packs for unlimited grenades, ammo, and rockets for you and your teammates. Mortar which allows you to destroy vehicles and spotted enemies fast and light to heavy vehicles. Slow to fire and slightly inaccurate but has no tracer and is usually at least a heavy blow to an enemy if not a kill. usually takes a hit to a tank to disable and two to destroy it. C4: able to stay stationary with the detonator in your hand able to kill anyone who comes even close to the explosives. Large splash damage, able to destroy anything with two packs of C4, but obviously requires placements. Good for ambushes by objectives and others that need support.
In my opinion I would choose a sniper but for you I would suggest support.