WD is amazing DPS as well, when decently geared, and has a "tanking" option with the bears (depends on what you want to farm of course)
I think someone's already addressed that the WD and the "bear" build is viable for farming goblins, but as for clearing through anything but Act 1 you're in for some serious trouble. Zombie bears has way too short of a range to be viable in Acts 2, 3, and 4.
Witch doctor can progress through acts, but its very slow/painful/frustrating because you're going to die...a lot.
Just wanted to clarify that Zombie bears does not actually tank any mobs after Act I.