i dunno about what u should do for ICC specifically. but im a devoted tank on my DK so i have 2 tank specs. frost AOE for trash. or bosses with alot of trash. and blood for single bosses or 1-3 targets. reason being is frost holds better aoe agro while blood has better single target living status. ur death strikes and blood abilities not to mention vampiric blood all give you an advantage.
Personally I'm a Blood tank. But almost every DK has his favorite. You gotta pick which one you like best. That's why I love DK's so much, there is no specific spec thats the best, I've seen all 3 do some crazy shit.