I'll be different and vote for the Disneyland version. True, the effects are better in the WDW version, but the exterior themeing, stretch rooms that actually go down and higher quality loading area push the DL version just ahead of the WDW version for me. But not by much. Unlike Pirates, they are both excellent and not to be missed and while Pirates is my favorite ride at Disneyland (just barely) the Mansion is far and away the best attraction at the Magic Kingdom and second only to the ToT in all of WDW for me.
Doesn't hurt that the DL version transforms into Haunted Mansion Holiday every year at DL, either!