On The Waterfront, A Streetcar Named Desire, and even to some degree Last Tango in Paris are as good as screen acting gets. Brando's intensely volatile prescence created a primer for Al, Jack, J.Dean, DeNiro, Caan, Depp, and I'm sure many others along the way. The guy was electric in all these films. His approach was as unique to acting as Frank's was to the Great American Songbook..

If  Frank set the standard for popular singing, then Marlon did it for screen acting. Frank was a unique alternative to the croonings of Crosby and Columbo in his heartfelt song renditions. He lived within the song as Brando lived within the role. You could say (and I will) that Sinatra had a Stanislavskian approach to a song, living and breathing the composer's story just as Brando did for a screen character. A method singer if you will.

Even at his worst ( Candy, Burn, A Countess in Hong Kong etc. ), he was always interesting to watch. He was still Brando.  Even at Frank's worst ( Feelin' Kinds Sunday, The Old Master Painter, and Mama Will Bark etc. ) he was still Frank. ( Well, maybe not the last title ). If Frank was the alternative to the crooners of the day, then Brando filled that role with HIS contemporaries as well. It doesnt mean Marlon was better than Cagney, Flynn, Tracy etc. It's just that his approach was different from anyone before him.

Gene Kelly once said that he considered Astaire "the Cary Grant of dancing" and himself "the Brando of dancing". Not better, just different.

Brando and Sinatra both brought a defining  individuality to their respective specialties. Like I said in the header, this is just my take.

Rick Apt