There's no way I could pick just one. I love Stephen King. I love his books, his movies, him, his wife's books, everything. I haven't read a Stephen King book I didn't like, and I've read at least 35 of them. If I had to choose one of them to be my absolute most favorite I guess it would be a toss up between Insomnia and Cell. For scare factor I would say Cell because when I was reading it, I refused to be anywhere near a cellphone. And things just don't scare me that much anymore.