Howl's Moving Castle.
The book is great, but lacks energy in its 2nd half and never feels like much happens. The movie completley changes the books plot in the 2nd half (you can actually see the exact moment they diverge) and makes the 2nd half more dramatic and have purpose. I love both, and they complement each other well as knowing what the book was trying to imply with Sofi helps you understand things the movie doesnt make very clear. But the movie is better.