My boys (8 and11) both prefer non-fiction. They love to read reference books and bookmark their favorite pages with post-it notes. DS8 also reads a lot of fiction because he reads constantly, but he rarely reads fiction outside of the fantasy genre. My DD15 also read a lot of fantasy at that age, but little non-fiction. I think that it is much easier to find appropriate fantasy novels for highly advanced readers than it is to find books in other genres of fiction.