Huzzah mentioned this and I’m going to restate.  The answer is undead.  I don’t care how funny the troll sillies are, the undead racial abilities are far better than the trolls, not to mention the spells. Plague is tremendously powerful (though mana inefficient).

If you are in a tough Player versus Player fight, dropping plague is on the path to victory.  Touch of weakness (which can no long be procc'd off of a wand) is an inexpensive way to make your job easier against bosses (most bosses are NOT immune to it). 

These two spells plus Will of the Forsaken, and the fact that neither the troll racial abilities nor their spell are worth a darn... done.

I’m sorry, I love the way trolls look, I love their sillies, but their racial talents and spells suck. One of my biggest regrets in World of Warcraft is chosing Troll as the race for my mage (lvl 60 frost).  Every single time I get feared, I look for the Will of the forsaken button and cry.