Mark of Blood I vastly prefer to CE, though that is a matter of threat vs survival.
Mark of Blood is only as good as your application of it, while CE is only good for trash with corpse volume. There's not a LOT of bulk trash in Ulduar like there is in Naxx, but I've made good use of both abilities.
Your spec looks sharp, the only thing I'd question is Scent of Blood. Personally, spamming single rune moves has plenty of RP stocking up so I am never unable to pop Mind Freeze, IBF, or RS whenever needed. Beyond that the only dump Blood tanks have is DC, and that's a fairly lackluster thing to spend on. Also with the single rune spending there are very few rune blackouts, and that is the only time I find it worth it to actually use DC. If you have a rune available you can always do better.