Gnome - (snare removal, arcane resist, 5% extra mana)
Dwarf - (Disease, poison, and bleed removal + temporary armor)
Night Elf - (stealth mechanic, nature resist)
Draenei - (heal over time, spell hit, shadow resist)
Worgen - (sprint, 1% crit, nature+shadow resistance)
I myself will be going Worgen for the sprint. Being able to gain distance on someone or escape from an unfavorable situation faster seems to be optimal (LoS-ing in arenas), though I must admit having shadowmeld would be interesting for Rated Battlegrounds.