How high quality gear can you get for the shamans once they reach 70? Xbox's got some really nice stuff. Five-Shaman PvP has more visual Oompf to it in PvP than 4lock1priest, but you have to do a bit more work to kill people.

Personally I think it's up to wether you'll want to run instances and heroics on your own for farming gold and gear, or if you want to be a god in pvp and AE farm with coordinated Seed spamming warlocks.