Always go with mage, in pretty much every game, until I've defeated it on every difficulty. Then I start having fun with other stuff. That's the cool thing about a party-based game like the DA series, you can get a taste of each class even without playing it.
Last play-through I used Sten, Zevran, and Dog, which was was actually a really nicely balanced party, I had like 15 different auras going (including cleansing aura) and hardly ever had to click anything. Sten and Dog together did some serious work, I just set them to attack the same enemy while Zev ran around incapacitating everyone. I've said once, I'll say it again, one of the only video games where you get a dog who's both lovable and combat-efficient, and damn what the forums say.
This time through I'm running with Wynne, Leliana, and Sten so far. Kinda not goin so great, I am playing on hard though. Leliana's pretty terrible if main char is a ranged caster like me. I'm hellbent on getting all the treasure though and she's the only pre-set with any sort of skills in lockpicking so far, don't remember if anyone else comes with them.
In other video game news... the man and I just started Hell mode on Diablo 3. I think I'm gonna try to craft the staff of herding without him just so I can see the shocked look on his face when we enter Whimsyshire