You left out the very best one, Return of the Jedi!!
In my opinion the order of quality pretty much goes in reverse order of episode number.
Return of the Jedi is the best of the whole series, with a beautiful conclusion.
Empire Strikes Back is an excellent movie but leaves you hanging (naturally)
A New Hope is classic, of course
Revenge of the Sith is definitely be best of the prequels, very enjoyable.
Then I would depart from the order slightly and say that Ep. I was slightly better than II. Attack of the Clones was just so poorly done in key areas like the romance sequence. Star Wars is such a great epic universe, I feel like they could have done something better / more believable / less cliche with that whole theme. Anakin was so whiney and emo. Amidala was so, well, whiney and emo in a female way. I wish Lucas had written that storyline decades earlier or someone good at epic romance and/or fantasy history had helped him.
Basically I am on this forum just to keep my lists from being deleted, which are very out of date. But I'll get back to them eventually... like next time I move ;]