Favorite current attraction: The Haunted Mansion - For me, Haunted Mansion is everything a haunted attraction should be. It sets up a mood that is dark and dreadful (ghost host's suicide, Constance's habit of dispatching her husbands, someone about to be buried who's not completely dead yet), but augments it with lighthearted whimsy (Hitchhiking Ghosts! Singing Busts! Mummies having Tea!), and in doing so, it can be scary enough for horror buffs, but also retain a family-friendliness.
And in an era where "haunted house" generally means "psychopaths chasing you with chainsaws and trying to be EXTREEEEME!", Disney's version is VERY welcome!
Runner Up: Tomorrowland Transit Authority Peoplemover - Because it's rarely crowded, it's relaxing, and because I'm always tempted to repeat the old Pete Renaday spiel as A.I. conductor ORAC-1
"NOW APPROACHING SPACE MOUNTAIN"
Favorite extinct attraction: Horizons
Runner Up: 20,000 Leagues Under the Sea Submarine Voyage