I'd like to see what the historians here have to say. I'm still working on my list but I think I have fullmer number 1.
Gavilan, LaMotta, Basilio are the main 3. Fullmer and Olson are the next category but I'm not wholly convinced they're any better than wins against Armstrong, Zivic or Angott.
Zivic or Olson. But Olson not ATG. Nor would Maxim have been had he beaten him. Hmm. Having a hard time here. At least you don't discount the Graziano win
One thing I noticed about Ray Robinson was he folded like a lawn chair when he came to the UK and fought journeyman Randy Turpin. I believe that's why Mayweather avoided coming over here because the likes of Brook and Khan would use him merely as target practice when he'd been properly tested by the BBBoC.