If I could choose completly free I'd roll a Warlock. A arcane magic-user that (unlike mages) has it's abilitys from a magical being/creature somewhere in his bloodline (a certain dragon-race in my case). They're far more skilled in the use of normal or exotic weapons than mages and other arcane magic-users because they don't have to spend their time studying the arcane forces and laws, and thus have time to master a weapon of their choice.
Holy cow, an MMO where I could be a lion or a dragon? Yes please. Shoot, why not make it a lion-dragon-thing? Sounds like fun. As for what I would do, I would do the same thing I do in all MMO's . . . be on the front lines absorbing the damage from monsters.