Personally I chose undead because people love to aoe fear multiboxers. I get feared about 3x as often with this group than anything else i played solo. Now when I see a class capable of fear bombs running towards me I just pop will of the forsaken so they get to see "immune" pop up on all 4 characters

My choice for anything that can't be undead would be tauren. Health is always good, and aoe stuns are viable anywhere.

As for class... anything but melee, except maybe for your main