Personally i love the idea of the druid heavy teams. So the DK or Druid tank.

I think they could seem a bit too much like the shaman. There would be awesome power available if you can mouse broadcast with your solution. Making full use of treeants, hurricane and starfall to blow things up.

If you like a bit of pvp then I'd go for 5 druids.

After that I'd probably try a 5 paladin group. Lots of buffs, auras. Speedy movement everywhere.
Resses, emergency lay on hands. Bubbles.