The book is better 97% of the time (The Godfather and One Flew Over The Coocoo's Nest are in that 3% exception). Books are a different medium and you can do more with it.
Movies are their own medium and meant to follow a specific rule set if you want them to be good (no, 'content' slop don't count).
I'm going with 'Heat'.
The movie was originally supposed to be a TV show that would've stretched out multiple episodes. The supporting cast were already well developed characters. In a book, you could explore this further with the detectives and Neil's crew. The last time I re-watched this movie, I noticed that Ashley Judd's character had an interesting backstory with cheating on Val Kilmer and getting mixed up with that Jersey guy.
Casino would probably also work better as a book. The movie leaves so much out, like Frank having 3 casinos in real life instead of the sole tower in the movie. That was done deliberately to be easier for viewers to follow the film story.