I play mostly medic/assault/support. Mainly because revives/ammo are invaluable, however if a tank rolls up on my shit I'm going full on assault until it's down.
I will also play what helps the group most and I hate snipers. Even though you can run and gun better than medics if you can aim, increase that CoF DICE if they're standing and firing you twats!
I've played that mode and it's great, but they need to remove Mortars from that mode. You always get 3 or 4 people per team just killing you over and over again with no way to fight back, it is infuriating. It is by far the best game mode though.
They need to make it it where the attack and defend switch, like counter attacks or whatever.