I would do the druids. you might want to run 3 ele shaman, 2 boomkins and 2 resto druids. Be nice to have 6 trees, starfall, and more AoE.

But id keep it simple, and run 5 ele and 2 resto druids. Make some macros to have both druids start stacking hots on your main, another to heal whoever is getting focused, and fill the rest with AoEs. You'd be unstoppable.