Quote Originally Posted by Ualaa View Post
Horde = Blood Elf (Instant-cast Silence, off of the GCD)
Alliance = Human (Free Trinket, 2/3 min CD)

If you want to be mechanically the best.
Not saying others will not work exceptionally well, but hard to beat those racials:
I think Draenei have to be in consideration now too, specifically for multiboxers. Gift of the Naaru now/will scale to 20% of the targets HP and it stacks.