I went for three warlocks and one mage to keep my priest company.

Sure, Warlock AoE is a bit weaker than mage AoE, but not that much. All chars do single target and AoE damage. The warlocks have soul and health stones to offer alongside their pets and the mage comes in handy with water, arcane billiance and portals.

I find that my three felguards are fine for tanking duty. Tested up to boss 2 in the Slave pens so far. Having three means that you can afford to let one or even two drop. Redundancy is a nice thing =]

Have fun picking your setup of choice!