the latter is more full featured, but slower to launch and more complex to navigate through. I think I like Box Office.
It's tough. I like the BoxOffice icon (for some reason that matters to me), and the rotten tomato ratings. Movies.app's icon is horrible, and the interface isn't quite as seamless but I like the ability to watch trailers and get more movie info.
I hope to see an update to BoxOffice to add some functionality, and then I can remove Movie.app.