My favorite is definitely the original Star Wars, I can watch that over and over, because it was the only standalone movie, and it definitely the most fun SW movie to watch. You can watch that movie, without caring about the redemption of Darth Vader, or wondering about all the tie-ins of Jango Fett to Boba Fett, Luke being related to Leia, whose father was Vader, and Anakin creating C-3PO, it is what it is, and it my favorite movie of all-time.

Although I do think ESB is a little better than the original, not by much, but it didn't need to set anything up with the characters, so the movies get going from frame one. Thus, every SW movie is inferior after that.