Great thread.
Very tough questions because there are so many terrific performances there. The cast is uniformly excellent.
Brando is iconic. Pacino is brilliant. Caan steals every scene he is in. Duvall is his consistently awesome self. Cazale kills a relatively small role and makes Fredo seem like a fully fleshed out character. Keaton and Shire are both terrific. The list goes on and on to great supporting performers like Castellano, Abe Vigoda, Sterling Hayden, Alex Rocco, John Marley.
If I had to choose, it would probably be Pacino because he has the most to do and, if you didn't have him selling Michael's transition from affable, idealistic dude to irredeemably immersed in the business he was not supposed to become a part of, you don't have the essence of the film. That said, I think Brando is right up there with him and I personally have always loved Caan's performance as Sonny.
Cazale's story just makes me sad. Here's a dude who was in, what, five movies? And every one of them was a best picture contender and, in three cases, a best picture winner- The Godfather, Godfather Part II, Dog Day Afternoon, The Conversation, The Deer Hunter. Some absolute classics right there. The poor guy gets cancer at a young age and dies. Just horrible shit. I bet he would have accomplished so much in his career had he lived into the 80s/90s and beyond. Pretty sure he was engaged or in a long-term relationship with Meryl Streep at the time of his death.
