You don't want 2 close combat melee in the team - are you willing to live with one?

I've not dual boxed arena but a heavy melee with a healer that can take a pounding sounds interesting.

A DK, or ret pally or warrior backed by a healer.

If no then you are down to using ranged combinations.

e.g druids (moonkin), mages, warlocks, priests, hunters

2 of each or some combination of the 2, or 1 of the above and a pally healer.

Ultimately do any of those classes or combinations interest you.