Having exhausted the limits of what is doable with a Preist & 4 Mage team if I could go back 18 months I'd pick Shaman. Once I hit the Outlands the over all experience went downhill as my team was just way too squishy. Granted a paladin makes it a bit more viable, but even then you're relying on your main to be tank & healer. Arenas being what they are today I don't even bother. My team has been reduced to grinding dailies to give away epic flying mounts to friends and feed my prot warrior.