Hard to chose really.
Depardieu played the role of his life in "Cyrano de Bergerac". Best single acting performance ever AFAIAC.
"Amarcord" by Fellini is incredibly beautifully filmed. It has everything also : emotion, humour, poetry and the nostalgy for an era that is no more. (hence the title "Amarcord", meaning "I remember " in romagnolo dialect).
"Once upon a time in America" has to be the best gangster movie ever made. The only movie where De Niro, though excellent himself, is actually "outacted" (by James Woods).
That's just three that come to mind but there are so many more of course.