Some people seem to have great success with melee classes but starting out I would use casters first. The most important thing for me is a ressurection ability. If youre doing PvE and especially instances the benefit of 4-5 self resses especially when youre learning a new boss is great. Every boss, even those your fought before on single boxing btw is a new boss when youre multiboxing.

If you really dont want shamans then at least one toon that can ressurect is very useful - GY running a single guy or 2 is a pain in the ass.