There are a couple of good choices, and it mostly depends on if you have to Teleport or not.
Need to Teleport:
Lightning Sorc (fewer immunities)
Javazon (hands down)
These are all based on my opinions, experience, and statistics from the Ladder (A Trapsin and, I think, a Lightning Sorc were among the first to hit 99).
P.S: A WW-Barb tends to...not work so well. Theoretically it could, but the need to engage in Melee, and the fact that Baal is constantly Decripfying you...casters just have repetetive PvM killing down way easier than Melee guys.