Basicly Bliz design is Horde = Pvp, Ally = Pve

Hordes Racial Traits
Tauren = AoE stunt 2 sec, HP 5%+, +15 Herb, +10 Nature Resist
Orc = +25%dmg/-50%heal, 25% resist stunt, Pet +5% Dmg, +5 Axe
Undead = WotF, Carnibalize, Underwater Breath, +10 Shadow resist
Trolls = Berseking, HP regen, +5 Trowing weapon, +5 Bow
After BC Blood Elf = AoE Silence

Alliance Racial Traits
Human = Perception, +5% Spi, Diplomacy, +5 Sword, Maces
Dwarves = Stoneform, +5 Gun, +10 Frost resist, Find treasure
Night Elves = Stealth, + Dodge, Faster ghost lol, +15 Herb.
Gnomes = Escape Artist, +5 Int, +10 Arcane Resist, +15 Eng
After BC Dranei = HoT Heal

My Opinion - Left most is the best

horde:
warrior = tauren, ud, troll, orc
shaman = tauren, troll, orc
hunter = troll, tauren, orc
rogue = ud, orc, troll
druid = tauren
priest = ud, troll
mage = ud, troll
warlock = ud, orc


alliance:
warrior = All ok
paladin = human, dwarves
hunter = night elf, dwarves
rogue = human, gnome, night elf, dwarve
druid = night elf
priest = dwarves, human, night elf
mage = gnome, human
warlock = gnome, human