Tank: Warrior is not better for single target threat on any fight with aoe damage, undead or demon boss. His gear in T4 just give him more defensive stats. In later content he falls down to being useful for RoS only.
Healers: If you can have a raid with just rsham healers that is the way to go.
Utility: rShaman.
Since in TBC resilience contributes to the "uncrittable" cap along with defense, I'd pick Feral druid to tank, especially in the starting content. The reputation PVP gear you can get from the factions at Honored have a lot of stam and sockets as well, along with resilience, quite easy to get good enough gear to be able to tank heroics on a budget (not to mention the 2h mace you can get from Cenarion expedition at exalted rep, that thing is awesome).