I would have to say Goodfellas. While they are both amazing movies, I always found Goodfellas to be a more interesting story. If you have read the book Wiseguy by Nicholas Pileggi, you'd know that Goodfellas is almost exactly ripped directly from the book with very little changes to the story. Whereas if you have read the book Casino, you'd know that they changed a lot of stuff in the movie. Also in Casino, they added a lot of stuff from the book that had nothing to do with Vegas or the timeline of the movie. For example, there's the scene where Joe Pesci's character Nicky and his boys put that guy's head in a vice and pop his eyeball out. That actually happened in real life, but it occurred way before the time it did in the movie, back when Anthony Spilotro (the guy Nicky was based on) was still a mob enforcer in Chicago. Overall I just enjoy Goodfellas more, even more now that I got the 2 disc special edition with commentary by Henry Hill. I would highly recommend to any fan of these movies that they also read the books, because there's a lot of stuff in both books that didn't make it into the movies.