Without a shadow of a doubt, it's ESB that claims my heart for best StarWars movie :D. Don't get me wrong, I loved RotJ, especially the "Sail Barge Assault" but Empire was the film that just flowed so naturally - everything that was in it just felt appropriate and as if it belonged. I love each of the OT movies to pieces but there are certain small sections that seem to "drag" a bit more than others, but ESB seemed to all but eliminate this...
As far as the new trilogy goes (and I've watched both with a room-mate tonight ;)), AotC is significantly better (movie-wise) than TPM! Speaking honestly, the only
really significantly good thing to come out of TPM was the "Duel Of The Fates" score - that was quite simply awesome!
Whilst I'm on the topic of musical scores as well, ESB trounces its rival in that trilogy hands-down. Albeit most of the character's song motifs (not to mention atmospheric scores) were established in ANH, it's in Empire that really embellishes upon them and makes them shine
Movie Order Verdict:
* ESB (voted for)
* RotJ
* ANH
(would score higher if there was more Alec Guiness dialogue)
* AotC
* TPM
Well that's my tuppence worth

- that's what you get when you ask my opinion on something :p
-Jackpot