I would argue with you...Brando in the Godfather was better.
Brando certainly was good in the Godfather, and I don't want to suggest that he wasn't, but he really wasn't much of a factor in the second half of the movie. And I found the role pretty one-dimensional. Next to Pacino, Duval had more screen time in the two Godfather movies and his emotions were much more subtle, Tom Hayden was my favorite character in the two Godfather movies.
Brando was the best, but I think Duvall was far better in the first two Godfather movies than Pacino.
Brando sleep-walked through most of his movie roles. A GREAT stage actor.