The Exorcist is 1) the greatest horror film of all time, and 2) the most unsettling horror film I've ever seen. I've written extensively about that elsewhere, if you're interested (see below). :)

https://fanfare.pub/my-journey-of-faith-and-the-exorcist-84a74de51846

On the other hand, in my novel Death Nest, the film Serpent's Nest turns out to be pretty run-of-the-mill in terms of scares (I invented the faux-hysteria purely for this piece). Except for that one shot I mention, of course...