Video games since you can replay them and have more or less different results each time while movies stay the same each time you view them. Books are a close second since each time you read one, you do it with a different view.
I am really not big on movies, though I like them occasionally. Books - my attention span is too short for that. I appreciate books, but I would have trouble finishing even a book that is of my interest. I usually freeload in English class and never really do much of the reading.
Video games, though I don't play them anymore (I've got chess and GAG), would be the most fun out of those three.