In terms of how much they can offer, Amumu. The guy's ult changes a fight easily..

I read one mention of the so called "true tank" leona. I like her, but this thread reminds me, is she really a tank, or just an aggressive support?

Volibear's pretty good.

Shen and Malphite are both broken. Pick one of them, but don't expect to have that much fun.

Malphite and amumu. Amu's stuns are insane in a teamfight and malph basically does the same thing except with a knockup and some move distance.

Nunu is the best tank champion in my opinion, he can take a lot of damage and is one of the better team fighters because of his ability to slow down enemies and speed up allies, not to mention his devastating ultimate.

THE five best tanks in no order

Alistar
Malphite
Shen
Leona
Maokai

Honorable mentions
Amumu
Singed

what about jarvan

I mix it up, I usually play shen malph or singed in dominion. Shen when I think my team needs some epic supports, malph when I want the enemy teams ad's to cry, and singed when I feel like TROLLOOLOLOLOL