if you only ever quest then nothing beats hunters, they are never oom and even if they are they keep on fighting.
the problem is that once at 80 you will want to do dungeons and they aren't that practical for it.
the same for a mage priest team.

I would think these teams might be pretty cool in PvP.

for instances at 80 you will want the classic 3 dps , healer, tank though.
I love my shaman/pally team but I wouldn't mind having a second team that included a warlock, mage, druid, priest , pally... just to try it all out.
I bet the macros on a all different team are not as easy as it sounds, warlock and druid dps needs time to get going, to get all of the buff/debuffs up.