Convoy, because you don't have to be attached to a medic to do well. Anyone can run across the map and start messing stuff up, and I mean ANYONE. All the classes have a role that can be filled on Convoy. Plus axing the snipers is about as satisfying as it gets.
Gravelpit is fun. I play Dustbowl as well, but I don't think Dustbowl was ever meant to be played with 32 players... Sometimes it is so spammy I have to leave.