I wondered about this. Films like Howl's Moving Castle aren't the usual sort of things I watch, but even I could see it was well made anime. And it seems impossible for there to be a superior version of it in another format. Plus, I don't think I've heard anyone else mentioning the book. So, I think that there must be something specific to you which makes you like the book. Although maybe the person who chose to make the film was equally impressed by it.