OK, my criteria for P4P is not wholly academic, nor numerical. It is decided from the following process: Take fighter in question, assess their principle strengths and weaknesses, then just take him to different weights (in your mind) and apply his attribute sets against the best in that weight class, and come up with an honest prediction of how you think they would fare. Then you have to also decide your definition of 'greatest' is tied up with victory? Roberto Duran is ine of the alltime greats, yet his most famous fights are losses. His courage and durability earned him his place, not so much the outcomes. Moralles is undoubtedly a name that will live on as long as Barrera's, despite losing their trilogy.
For me, right now, Ricky Hatton is my P4P choice. He cannot be matched for workrate, grit, natural aggression, durability or character. His power is not causing as much trouble to his world class oponents as it did domesticaly, but he still has amazing power from round 1 right through to 12. He can toe to toe, he can spoil and tough out a decision, or he can box with timing and skill. His love of a battle leads to him being drawn into situations he could avoid, but thus far he has always had the cojones to come out on top.
He is the closest thing we have to a vintage 50's prizefighter competing today. An oldschool treasure to be enjoyed at every opertunity.