In my opinion, sometimes the book is better. Sometimes the movie is better. Sometimes reading the book and watching the movie are pretty much the same experience. And sometimes, on rare occasions, both experiences are valuable and if you're only doing one, you're missing out (for example, The Princess Bride or The Remains of the Day).
Buzzfeed put together a list of book and movie combinations and asked readers to rate them one by one, which is better: book or movie? You can vote yourself, right here. And let me know your favorite book/movie combination in the comments below!