Druids!!!

Thinking like this...

For instances especially if you end up doing heroics, you can have an extra healer so that the 2nd pally can tank or a tank so the 2nd pally doesn't need to tank . Boomkins don't have BOOM in their name for nothing so the damage is there, you'd also have 3x combat resses, which would be handy I'd imagine. Travel costs are cheap... (free flying mount?).

No idea about PvP on a druid though only played one on PTR and I sucked