I absolutely love his books! Still got a few left to read, though (and I can't wait to get a hold of them and read them!). I don't think I could possibly pick out one favourite. I love them all!
When it comes to the films, I haven't seen many of them - only A Walk to Remember and The Notebook, and I watched them both long before I discovered his books. But I enjoyed them enough to find the books, so I guess that counts for something