While you'll find lots of people who have watched and enjoyed every Harry Potter movie without ever reading one of the books, I've never found one person who's actually read the series and picked the movies over the books. How can you when the books are so great?
Don't get me wrong. I love the Harry Potter movies. They're some of my favorite movies in the world. Deathly Hallows Parts I and II were freaking amazing. But even they don't quite compare to the awesomeness of the books. This isn't really just a Harry Potter thing. I love movies, but I would always pick books over movies. I like being able to imagine things in my head. It gives you a certain leeway to decide things on your own. You have descriptions to go by, but overall, what things look like is all up to you. Get a group of people who've read Harry Potter, and each one of them will have imagined Hogwarts just a little bit differently. In the movies, you don't have that option because Hogwarts is given to you right on the screen. That's not really a bad thing. I love actually getting to see a version of Hogwarts, but it's not the same as the Hogwarts in my head.
Of course, we could also get into the changes that were made in the movies. The movies could never fit in all of the tiny details we get in the books. (Or apparently big details like the Marauders' backstory.) In the movies, we didn't get Archie and his nightgown, Remus rushing to Shell Cottage to announce Teddy's birth, or any of Winky's story. None of these things a really important to the plot, but they help make the books special.
The Harry Potter movies will always be special to me and some of my favorite movies. They're wonderfully made, and I love almost every single actor in them. The books just happen to be a bit more magical. I like that they give us small little details sometimes, and that they allow us to imagine things on our own. These things make it seem a bit more real and allow us to make the Harry Potter universe our own in some ways. None of us experience the books in quite the same way.