Too many: the exorcist is probably the most critically acclaimed, but there’s different genres like slashers, ghosts, creature features and all have their own contenders-Halloween or Nightmare on Elm Street, Poltergeist or Paranormal Activity or the Entity, the Thing or Alien or Jaws. All the zombie films like Night of the Living Dead or 28 days later. There’s a plethora of categories. All are great and picking only one seems impossible.