Rather than the superstars I would go with the guys who were never in a bad fight like Gatti, Chacon, Boza Edwards, Limon, Ward, Morales etc, no BS battlers whose fights you want to rewatch.
I've come to form the opinion that these are the guys with a good case as the GOAT, so I'll put them Armstrong Ali SRR Greb Langford Louis Charles
Mike Gibbons, Henry Armstrong, Benny Leonard, Joe Louis, Ray Robinson, Archie Moore, Tony Canzoneri, Harry Greb, Marvin Hagler, Eder Jofre, Fighting Harada, Jimmy Wilde, the first Muhammad Ali.
Oh! This looks like you're trying to make a Mount Rushmore of Boxing. I have 2 actually. Mount Rushmore for All-Time P4P Fighters: Harry Greb, SRR, Langford, Armstrong Mount Rushmore for All-Time Greatest Boxing Champions (I chose 2 great P4P champions and 2 great HW champions): SRR, Armstrong, Ali, Louis
Some great responses! I don't really have a solid P4P list - I guess the usual guys that are almost always at or near the top in most lists you see would be my pick and they've all been mentioned already. Greb, Armstrong, Langford, Robinson, Charles, etc. I'll throw Ali in there as he holds the distinction of being the one fighter that has the highest likelihood of defeating any fighter that ever lived regardless of size, style or era.