Max Imp. TCLap. It's far and away better than, say, Unbridled Wrath + Piercing Howl is going to be in raids.
I've never been a fan of Imp. Sunder for a raid tanking build. It's not all that useful - you're going to be throwing Devastates after the first few seconds, and the slight difference in TPR until that point isn't really a factor.
I'm more a fan of something like;
http://www.wowhead.com/?talent=TV0cZVZbytsh0zfest
It's a little more balanced and gives you a lot more strength in Heroic 5-man.