Best is a relative term. While I wait for your armory to load, I'll shed some light on this.
Blood: Best EH and single target threat, low AoE threat. Makes healing you a breeze, but on trash, unless you're real good, you're bound to lose a mob or two. This is from my personal experience.
Frost: A Godsend for new tanks. Huge, front-loaded AoE threat, decent single target threat, and imo, the best mitigation in all three trees.
Unholy: While I haven't tried this spec myself, it seems that Unholy's falling behind in threat, and the mitigation leaves a bit to be desired as well unless it's a magic heavy fight. This info I've gleaned from threads here on tankspot.
As for gear, you're golden. Your target stats haven't changed all that much. Look to be about Ulduar10 ready if I'm readin' it right. Maybe Ulduar25 and ToC10.
Specs and glyphs: Go with what you like, and glyph accordingly. That's the best I can say. Just because Blood has the best effective health, thus the best potential, doesn't mean it's the best for YOU. Personally, I prefer Frost because it's more fun. Some people still roll Unholy tanks and love it. Just do what you feel is the most fun, then the rotation can get nailed down.
...Thoughts of a philosophical Death Knight...
If death is the inevitable end of life, is life the inevitable end of undeath?