Definitely melee. I tried a mage upto lvl30, got bored as crap with it, rerolled sword and board, absolutely loved it. Now level 50ish and still get challenges with it, where as the mage was a walking godmode even on master with stunlock.

I feel the game was absolutely "built" around melee classes. The others were just tossed in for flavor. Still it's nice to have choices.