I personally think ROTS is the best prequel and AOTC is the worst prequel.

This is my current ranking of the main saga movies, best to worst:

The Empire Strikes Back
One of the best movies of all time. Almost every aspect of it is amazing.
Star Wars
A great movie, although it’s not as good as Empire.
Return of the Jedi
A good story that was unfortunately mixed with burp jokes and teddy bears.
The Last Jedi
A mixed bag. Some parts are great, some parts are terrible.
Revenge of the Sith
Less boring than the other two prequels, although the acting and dialogue are still bad.
The Force Awakens
A derivative corporate product that only exists to make fans nostalgic.
The Phantom Menace
The good elements of the movie are overshadowed by the boring story and bland acting.
Attack of the Clones
Almost unwatchable. The story is boring, the acting is bland and the dialogue is awful.