From a Troll Moonkin perspective:
PVP: Tauren stun can be a lifesaver. However the mini troll bloodlust is nice to get some rapid self heals, or burst a dps down whilst the healer is in a root/solarbeam. Theres a lot more you can do with the troll racial, but the Tauren is simple and very effective.
PVE: Troll hands down.
But if your gonna roll herbalism I'd go Tauren.
But the troll Moonkin form looks cooler than the Tauren one.
*shrug* Go with what you like.