Warrior. However, for farming when it first came out, I was also rockin a DH and enjoyed that a lot too.
I have always been a ranged kind of person. Of the three, I'd have to go for mage. I didn't really like the witch doctor. It's image is also unsettling to me. Mage's make farming so much easier.
In Diablo 3 my favorite class has to be the witch doctor. I'm a huge fan of pet/summoning classes in games, and while I sadly can't amass a giant army of skeletons to fight for me, it's still the closest the game has to that archetype along with it being an enjoyable class to play.
