If you go by critical reception, Revenge of the Sith is the most well-received Star Wars film.
Not trying to start a fight, but I'm not sure where you're getting this from. Of the prequels, yes, it was the best received by critics, and got a generally positive review. However, compared to the critical response of A New Hope or Empire Strikes Back, it pales in comparison. Also, RotS was only nominated for one Academy Award (which it didn't win). A New Hope was nominated for 10 and won 6 (plus a Special Acheivement award). Empire was nominated for 4 and won 2.
Edited by Kodiak3d