The Empire Strikes Back!
Along with the first showing (eighth in line), I saw it nineteen times during it's first theatrical release.
Ever since then, I absolutely enjoyed anything that took me out of my "comfort zone".

Revenge of the Sith (teh graphiczez...)
A New Hope (excellent but the terrible - by today's standards - effects pull me out of the movie)
Empire Strikes Back (nothing much to say, classic)
Return of the Jedi (Ackbar, his monkey sidekick, and those goddamn ewoks...)
Attack of the Clones (minus the story)
Teh phantom firststarwarsmoviein15years (the fight with Maul is pretty awesome, but that f***ing Jar Jar... )

Edit: the top three are pretty close. III is decent with modern graphics and some pretty cool fight/battle scenes, IV is just awesome throughout though again the effects are pretty offsetting, and I have to give major props to V for pulling off (probably) the only really good movie in cinematic history where the bad guys win

1. Empire Strikes Back(people who agree with this are intellectual)
2. New Hope
3. Revenge of the Sith
4. Return of the Jedi
5. Attack of the Clones
6. Phantom Menace

IIV
I
VI
IV
V
II

Empir.............. Wait this all seems very familiar. I think there's a glitch in the Matrix

http://www.vgchartz.com/forum/thread.php?id=98396

Anyone that puts Episode 6 lower on their list for the Ewoks should be hit...very hard. Sure, it had Ewoks, and a Tarzan-style Chewbacca. It also had some of the best dialogue in the entire series, and the first show of power by Luke Skywalker. And in case you put it at fault for something silly, look at this quote from Episode 4:

"Darth Vader: I've been waiting for you, Obi-Wan. We meet again, at last. The circle is now complete. When I left you, I was but the learner; now *I* am the master.

Obi-Wan: Only a master of evil, Darth."

Prequel-worthy, if I do say so myself. If you want to see a badass fight, and some of the best dialogue and character development in the series, look no further: