There are two that deeply affect me every time I see them.
Prince of Darkness is the first. A priest enlists the help of local college students when he discovers a bizarre green container under a decrepit old church. This is the most unnerving and creepiest movie I’ve ever seen. Everything in it is deliberately designed to make it feel apocalyptic and inescapable. People inside become infected with the essence of pure evil, and they can’t escape because there’s a horde of insane/possessed street people outside that will murder them if they try. Oh, and mirrors are utilized as portals to an evil dimension of pure antimatter, and if the main characters don’t stop the possessed inside the building, they’ll bring the demonic god of the antimatter dimension into ours.
It is a really creepy movie that works on atmosphere and terrifying dialogue. I highly recommend it, and the VHS dream sequences/premonitions are icing on the cake. Watch this late at night with all the lights off.
The other will always be
The Blair Witch Project. I hate the woods. I hate the idea of being stranded in the woods with no way out. So what better movie to watch than one in which the main cast literally
can’t get out of the woods because they keep shifting and preventing them from leaving. The Blair Witch mythos and iconography in this one is especially freaky, and so many scary moments abound here. It always feels like I’m watching a snuff film, and that terrifies me so bad.
A good contender for runner-up is
Paranormal Activity 3. The first one is good with some really scary bits, the second is mostly boring in my opinion, but this one is the best of the franchise and one of the best found footage movies out there. I really don’t want to say anything about this other than “family moves into haunted home” because the movie works so well with surprises, details, and twists. Just go watch it, preferably late at night and alone.