Probably Return of the Jedi for me as well. It isn't even in my top 3 Star Wars films any more but my gosh did I watch and rewatch that movie growing up. The Falcon skimming along the surface of a Star Destroyer, Scout Walkers marching through dense forest, Speeder Bikes, the Sarlacc Pit, the swelling music as Luke goes off on Vader. Nothing was cooler. And now with Revenge of the Sith its even better.
As far as movies I've seen the most in an actual movie theater, they are:
Fellowship of the Ring (8 times)
Terminator 2 (7 times)
Aladdin (7 times)
Star Wars (ANH) (6 times)