World of Warcraft weapon question?

I'm getting a powerleveling service for my WOW account (it's not cheap) and one of the features for my leveling package is to choose any weapon in the entire game, no matter how rare or expensive it is, and theyll get 1 of that item. Im a level 80 undead warlock. What would be like the best staff in the entire game? it needs to go good with tier 10.