Revenge of the Sith is the obvious best. The story is brilliant and for the most part the acting is good. Revenge is truly up to the standards of the original trilogy. It also is more powerful and has more emotion than any of the others.
Attack of the Clones had good story and the climax was good but the love dialogue was not so good.
The Phantom Menace is good too but Revenge of the Sith is the best of the prequel trilogy.