"Scariness" is a very subjective concept, so something that could be terrifying for one person might be a joke to someone else. Because books can't exactly rely on cheap tricks like jump scares or thundering sound effects, there is no way that they can scare you as much as a movie. With that said, if you have a good imagination then the stuff your mind can conjure up is way worse than any movie could ever match. A good example of this would be a book called House of Leaves by Mark Z. Danielewski. Everything about this book makes it unsettling to read as even the style and layout of the pages are done in an unconventional manner. It is one of the first books that I have ever read where the author was able to make me feel claustrophobic. What is even more amazing is that the author classifies the book as a love story.