I think at this point there isn't enough data to make a call. The big "ifs" in my opinion are:
Will there be IWT?
Will there be a balance pass, or will classes be as they were?
If you're after gold, then I imagine for the first six months of the server's life you'll want to farm humanoids for raw gold plus cloth drops. Tyr's Hand or running a group of 5 through dungeons might be the most lucrative.
As far as group comps go? With no balance changes and IWT, then Warriors will without question be the best class for everything. They scaled better than every other class with gear, and they were the best (read: only) tanks. Without IWT, then Mages will probably be the best. Even with the larger debuff limits, Warlocks and Hunters lagged pretty far behind Mages for damage; we should probably not even talk about Druids.
If they do a balance pass, then everything's up in the air. All of the classes were pretty trivial to play compared to today's standards, so pick the one with the best looking T2 set? :)