Knoebels Haunted Mansion was voted #1 by over a 3-1 margin over Spiderman.
While I truly enjoyed Knoebels Haunted Mansion and I think it's definitely a unique experience it's just not on the same level as Disney and Universal. Personally I would even take DCA's "Tower Lite" over the Knoebels Haunted House.
The top 10 list:
1: Haunted Mansion - Knoebels
2: Spiderman - IOA
3: ToT - Disney MGM
4: Haunted Mansion - Disneyland
5: Haunted Mansion - Magic Kingdom (orlando)
6: Whacky Shack - Waldameer Park
7: Indiana Jones - Disneyland
8: Splash Mountain - Disneyland
9: Haunted House - Funland
10: Pirates of the Carribean - Disneyland