Hagler would have the best chance of the four. At his best middleweight form, I think that's a near even fight, but I wouldn't outright favor any of the Fab Four over Robinson. Hearns would have the smallest chance imo, due to his durability issues and Robinson's absurd firepower and chin.
I would love to see the two sugars go at it at 147. Think Robinson would win close though. I have a hard time picking anyone above Hagler or Monzon at 160. I think they both could eek out decisions
Wouldn't put it past Hearns to outbox anybody at 147-154, even Robinson. I doubt he's afforded the opportunity for the duration though with Robinson a lot less content to circle the ring and exchange jabs from the outside; the combination assaults to Hearns ribs and head will be much more frequent and persistent and he's got the chin and recuperative powers to handle anything Tommy dishes out; I wouldn't consider the opposite true. Hell, Kid Gavilan could beat Hearns based on activity, chin and stamina without a fraction of Ray's power.
I would rank all of the fab four ahead of Jake, so all of them could beat him if things lined up perfectly for them. But Robinson beats all of them about the same percentage of the times he beat LaMotta.
Though none will hold the 16 lb weight advantage Jake did over Robinson in 1943. I'm assuming we are taking him at his Welter and Middleweight bests for Duran/SRL/Hearns and Hagler, respectively. He could feasibly fight and beat Hagler coming in under 147 and he'd probably have more in terms of his speed and reflexes being that it encompassed his peak, but I'm more comfortable sending in the early 1950s pre-retirement versions who came in around 154-157.
Lets put the fab 4 in HIS era for this. All too often we put older eras into more modern eras and that shouldn't be done, simply because **** was REAL back then. Real as in, grimmey ass refs letting LOTS of **** slide, and those thin ass leather gloves. Really rough clinches etc. I pick SRR to beat all of them. I think he knocks Hearns out at 147 without a doubt. I think he bangs SRL in a great war. He wups up Duran easily, but thats not a knock on Duran at all. I think out of all of them, Hagler gives him hell, because of pressure, and his chin. What a war that would be.
Herns and Leonard at 147 are 50/50 bouts. Hagler on one of Robinson's famous off nights at 160 same for Leonard and Hearns. Duran is dead in the water against Robinson.
Robinson is the best welterweight ever, Hagler is top 2 middleweight(him and Monzon IMO) Robinson cracks top 5 at 160 to. I can't pick him over Hagler though
An honest to fair projected pick for all of the fab four against the greatest of all time in Sugar Ray Robinson would be that all four of them at their best would win at least one match in a best of three fight series against Robinson. Sugar Ray Leonard, Marvelous Marvin Hagler, Roberto Duran & Tommy Hearns were all more stylistically polished fighters than those of Carmen Basillio, Randy Turpin, Gene Fullmer and Jake Lamotta, guys that were more than good in their own right and all who managed to win one fight against an either primed or still nearly primed Sugar Ray Robinson.
Only Turpin managed to really pull it imo, though a win against him from 1940-58 at any time holds a good amount of value.