<Lordaeron> What is the best tanking spec right now?

Hey I am looking to DK tank, and am wondering which spec is more viable. I thought it was primarily blood since its 3.3.5, but I am seeing a lot of guides that are for frost tanking as well. Is frost tanking at all viable or is it just something used for fun. What would be more useful in a raid scenario?

For single target (heavy hitting raid bosses) - blood (either with deep frost - frigid deathplate, or just regular one with heart strike).
For aoe howling blast madness (add fights or heroics) - frost (either dual wield or 2h).