Worst Warcraft Quest!
I have to respectfully disagree with Green Hills of Stranglethorn being the worst quest in the game. It may be annoying but it you can survive quite well just skipping it. IMHO the absolutely worst quest is from Wrath of the Lich King; Battle for Undercity.
Here we have a quest that you are given with no warning whatsoever, must complete or you can never do business in Orgrimmar or Undercity again, or much else. Then, when you finally figure out what you need to do it takes at least half an hour, often more than an hour, and is utterly pointless. As long as you stay near Thrall and Lady Sylvanas you cannot die, you don't need to make a single attack to succeed and the outcome is never in doubt.
It's entire purpose is storyline and it's annoying as all hell, even moreso if you have to endure it more than once.
Biting the hand that feeds IT
