As a visual learner there is much about the movie that speaks volumes in just a few frames.
So for me movies can tell a richer story than books can.
Though, I find myself admiring the book more.
Here's why.
From reading the book I learned so much about Life.
I have Asperger's which means I am socially retarded. I'm not Rainman, not as smart or as dysfuntional. More like Freddy (in the movie, not the book)
From reading the book I learned to pick on on people being nice and going the extra step to help out. I learned more about social interactions, and the subtleties lying beneath, from reading the book than I did from watching the movie.

They are both great. (I do admit, Puzo could've used a ghost-writer to make it a better, fuller novel; but great story nonetheless)