None of these.
More like mindfucking situations, when you feel the character's confusion and fear.
For example, in 1408, which is on of my favourite horro movies there's that scene where just when he's going to escape through the window he sees it's no longer there, that the reality he lives in has changed and no rules of logic apply. That kind of thing is what I find scariest. Gore, screaming, sudden scares, murders, etc do nothing for me really.