Which actor has a better resume in such a small amount of time? He only did 5 films; The Godfather, The Conversation, The Godfather Part II, Dog Day Afternoon and The Deer Hunter and all 5 were nominated for Best Picture plus he was engaged to Meryl Streep and then he dies of lung cancer.
As far as the OP's question these movies are my 1A and 1B for best ever. I give a slight advantage to Part II just because it seemed so original in the way it went back and forth with Michael's timeline and young Vito's timeline. To me one of the most iconic scenes in any movie ever is Michael giving Fredo the "kiss of death" and saying, "I know it was you Fredo, you broke my heart". In Part II you also get the Young Vito murder of Don Fanucci scene which is perfect and the Fredo scene of him saying, "I'm smart and I want respect" which would have been even better if he was wearing an Aggie t-shirt while he says that. That being said I could probably change my mind over and over and pick part I based on my mood but tonight it's Part II.