Before I give you my favourite weapon, allow me to explain why. In Skyrim there is a book called the Red Kitchen, which tells that a meal can only be as good as the setting, the events that happened during, before or after it and so on. A 12-course meal with dull company won't be remembered as well as a jacket potato with a loved one, for example. The same applies here.
The reason why Wabbajack is my favourite weapon of all is not because of its effects but the story before that would reward you with it. Sheogorath's dialogue was just as clever as it was in TESIV: The Shivering Isles (and the same voice actor to boot). Inside the mind of mad emperor Pelagius the 3rd, players had to defeat three challenges of paranoia, despair and fear. The challenges weren't solved by sword and sorcery like every other quest nor could they be completed prematurely by speech. Instead you had to cleverly use the Wabbajack staff to change a foe so Pelagius could conquer his dementia. It's not revealed if you managed to change the course of any alternate timeline where Pelagius was cured of his insanity, but it's nice to know that we've an insight more into the Elder Scroll's own Caligula character.
Upon leaving the subconcious of the mad emperor, I never used the staff because I found little use for it. While it is funny and gorgeous to look at (the tip of the staff has the three faces of madness), it went into my weapons container at my house in Whiterun. With my children there. Unguarded.
Oh, and there's a reference to Haskil. What a funny bloke he was!