Either adjusting for weight or not, who do you think would be the best boxer if he could fight in his prime? Why would he win?
I have left a third option of your choosing because, even though Marciano is considered the best and Robinson the best pound for pound, there may be others I do not know about.
I don’t think anyone considers Marciano the best ever. He’s mostly known for being undefeated. I’m not a boxing expert, just info I’ve absorbed through the years.
As much as a consensus can be claimed I think Sugar Ray Robinson is probably considered the best ever.
My choice would be Roy Jones, Jr., at his peak he was a machine. Speed, power, skill and style. I know looking back (and his later fights) at lot of people dismiss him but the video doesn’t lie, he was awesome.
Joe Louis. Longest heavyweight reign.
Marciano definitely not considered the best. Ray Robinson had been, but several modern boxers make that questionable. Roy Jones has been mentioned, Floyd Mayweather possibly, Pernell Whitaker, and many others in lighter weight divisions, Joe Louis and Ali as heavyweights. Andre Ward hasn’t fought for a while due to injuries but could end up on that list. Salvator Sanchez was heading in that direction before an untimely death.
It’s difficult to compare boxers across different eras. Title fights are only 12 rounds, the level of competition varies in different eras, the rules of the game have changed over time.
In the Silver Age of boxing, Robinson was definitely the best.