Ranking his performances:
The Godfather Part II
Dog Day Afternoon
The Conversation
The Deer Hunter
The Godfather
The Godfather Part II
Dog Day Afternoon
The Conversation
The Deer Hunter
The Godfather
The Godfather Part II -- arguably the finest performance in the trilogy
Dog Day Afternoon
The Conversation
The Deer Hunter
The Godfather -- honestly, I always forget him in the first one
The Godfather Part II
The Deer Hunter
The Godfather
Dog Day Afternoon
The Conversation
From the one's I've seen:
1) The Godfather Part II
2) Dog Day Afternoon
3) The Godfather (just didn't have a whole lot to do)