I think this one is pretty much a no-brainer. I have to admit, this is one book I actually saw the movie before reading, and enjoy both, almost equally.
The book has all the goodness of the movie, only more of it. Most of the dialogue in the movie is left intact, as far as I could tell (and remember). This is one of my favorite books to read out loud, and I have done so for a couple of classes and two groups in the woods, who love that I do the voices, because I can, awesomely. Obviously.