If you are asking what was the best final movie in a triology, there are so many to pick. Godfather part three was great, last crusade was, return of the jedi wasnt as good as it could be , return of the king was great , back to the future part 3 was ok, the good, the ugly and the bad was a great movie too. Its difficult to choose only one.
yea once upon a time in mexico blew, that one of robert rods worst movies ever, but he redemmed himself with sin city. In once upon a time they didn't even have the effects well done, you can see some guys shirt burning from "being shot" in one of the scenes. Terrible.
I don't know if its considered a trilogy because its possible their mayb be a 4th someday, but since there is only 3 right now i will have to say army of darkness. That movie is hysterical