Brando
I agree with the people who said the movie was a little too long, too slow in places, and with various other criticisms, but Brando is so RIVETING to watch, I was too entranced to care. I was just happy to keep looking at him and was glad he was in almost every scene. He really seemed to be trying to perform well, which later on, he didn't always do.
It was so much better than another western he did later, with Jack Nicholson, "Missouri Breaks," where he obviously didn't care anymore and was just fooling his way through it, until he could pick up his pay check.