In wow as a death knight is the blood talent tree or frost better for tanking or should it be doubled because hearing that in cataclysm blood talent tree would be for tanking which one is it

In Cataclysm, Blizzard is making the Blood tree the tanking tree. However, currently (since Cataclysm is not out yet) all the trees can be used for tanking to an extent. Frost is one of the better ones at holding aggro. Blood tanks can self heal while tanking pretty good. Unholy is the least capable of the three.