You going to use RaF bonus to get toons up then transfer to 1 account? Or are you planning on dual boxing for a while.

If you are wanting to move them to 1 account i would

Hunter/any healer class thats boring to lvl.
paladin/any healer class thats boring to lvl.
rogue/any healer class thats boring to lvl.

aslong as you have a main toon thats easy/fun to play the 2nd toon should have some healing capabilities.

If you are going to dual-box for a while i would try 2 of the same class
2 shaman
2 mages
2 hunters
etc.