Now that I've been playing this for a bit over a week, it's interesting to look at how much time I've spent on each class. I spend an overwhelming amount of time on the Sniper, Medic, and Soldier classes (in that order) and everything else is pretty weak.
I think I'm drawn to the sniper and soldier because each is sort of like the SS2 days (rocket whore and sniping). The medic on the other hand is very rewarding when you have the right team. Having played a cleric in DAOC, this fits my personality as well.
The achievements are fun to track as well. Rather than go to empty servers and "power level" them, I think I'm going to just play the game and enjoy the accolades as they come.
Anyways....having a blast. I'd like to hear others who enjoy the others classes and why.