Has Paul Newman’s legacy aged much better than Marlon Brando’s?

You could argue that Newman's best and iconic films were made when he was younger. He may have gotten better with age but those are the films he's remembered for. With Brando his iconic films cover a greater age range - even if there are some silly lazy roles towards the end.
But 'greatest of all time' is relative - I can remember when Paul Muni and Laurence Oliver, perhaps even Lon Chaney, were the recipients of that accolade.

Of course! Newman spent his later years getting better as an actor and raising bazillions for charity, while Brando spent his later years betraying his talent, gaining hundreds of pounds, and indulging himself in decadence and insanity.

Brando is the ultimate example of someone who had everything, and threw it all away. And of his own free will.

BRANDO HAD SOME SOLID WORK...BUT PAUL NEWMAN DROPPED AMAZING PERFORMANCE AFTER AMAZING PERFORMANCE INTO HIS 70S.

Newman leaned into his middle-aged roles very well and found the best performances when paired with a demanding director like Sidney Lumet. Lumet thought that Newman wasn't applying himself in "The Verdict" and strongly pushed at him, convincing him what a great part and what a great opportunity it was.

Brando just seemed to lose interest more and more after "The Godfather" and just seemed to treat roles more and more as jokes. That is the difference between the two actors.