9 is the worst. There's nothing redeeming about that show except for the Steiners/Headshrinkers match where they beat the sh*t out of each other.
11 pops up pretty frequently when discussing worst WM's, but it did have HBK/Diesel, Owen's first title victory, a decent Razor/Jarrett match, and Pamela+Jenny McCarthy in their prime.
I watched 4 recently and that was pretty bad as well. Its a great moment to watch as a Savage fan, but the rest of the show just drags and seemed like it would never end.