Blood has been a pretty solid choice since release, and has despite a few ups and downs never been a bad raiding spec.
In the beginning unholy was the only way to go, but raids were restricted to one UH death knight because Ebon Plague didn't stack. Then when UH was nerfed, blood was pretty much the only way to go. Frost hasn't been any good for ages, and from what I've seen so far, the dual wield buff didn't do anything to change that. UH was buffed this patch however, and I think it has beaten blood (which was nerfed in terms of cleave damage) on both single and aoe dps.
Take a close look at your gear. If it has armor penetration all over it, go blood. If it's haste, go UH. That's the best advice I can give, either works at the moment
