My favourite book has yet to be turned into a film. There was talk about Mitch Albom's 'The Five People You Meet in Heaven' being made, but nothing ever came of it. I am not sure if I want to see it as a film or not. I am always cautious of adaptations because they must invariably deviate from the original.
My other favourite books were turned into films before I was born, or I saw the film first (Peter Pan, Alice in Wonderland, Winnie the Pooh, Harry Potter), as a result, I ended up not being bothered by any changes that were made.