I've ran every heroic in the game without a tank they aren't needed, but never hurts to help. Lvling a 2nd group currently to start 10boxing kara. Going to definately have a paladin for this kind of stuff As far as the OP question goes. With RAF out you can lvl pretty much EVERY class quickly giving you more options with WOTLK comes out. You can mix and match or stick with the shamans. My favorite class is by far shaman, so they will remain my main through WOTLK.