I really liked the first one (a new hope), such a simple and complete movie. It lacked the complexity of some of the other ones, but made up for it with a great narrative.
The first one I saw was The Phantom Menace, at the time I was pretty young and easily impressed by CG on a big screen, so back then it seemed like a good movie. Let's say that I've only tried rewatching it, I seem to fall asleep every time.
I liked Attack of the Clones a bit more because of the guy with the double light sabre cause it was cool. However, it was completely forgettable.
Revenge of the Sith was kind of cool, I guess?
The Empire Strikes Back was meh and Return of the Jedi was bleh, even though right now I wouldn't rank them below episodes 1 and 2.