Definitely 'It'. It was a great adaptation of King's work. The movie was able to build tension and horror throughout. There was also 'Gerald's Game'. This film took the psychological horror route. It showed how the main character was trapped physically and mentally, with her own mind starting to play tricks on her as she was in a very vulnerable situation, all based on King's novel.
One is 'It'. It was a big hit in 2017. It has all the elements of a classic Stephen King horror - a small town with a dark secret, a group of misfit kids, and a terrifying antagonist. Another one could be 'Gerald's Game' which also came out around that time. It's about a woman who is handcuffed to a bed in a remote cabin and starts experiencing some truly horrifying things.