I loved Cho'gall as a tank. same for off tanking Maloriak hm as the add tank (mostly on 10, didnt like it as much on 25) Halfus hc aswell because of the high damage you did as a tank.
tier 12 I really liked Alysrazor because of the damage you did as the tank. and of course Ragnaros hc was an amazing fight.
in tier 13 it's mostly Zon'ozz I liked, little bit gunship but havnt been much of a fan of the rest.