Eric Morales. He never fought a disciplined fight in his life ('cept perhaps the first against Pac, but even there...) and still came out on top almost every time. Born a fighter. Born a champ.
I'll go out on a limb here and pick JMM. IMO JMM is better than prime MAB or prime Morales especially at 126 and above. Many cited Morales' win over Pac as proof but considernig the surrounding circumstance in that fight (winning gloves, nasty cut due to headbutt), JMM's draw with Pac was more impressive IMO. Even Roach said it over and over again, that JMM is a level better tham MAB and Morales and that was why he was so against it when Pac agreed to fight JMM in 2004.
morales, good and faster boxer...JMM's counter punching wont be enough, Morales has better offensive arsenals and an underestimated defense.
Which weight? At 126, I'd go on and pick JMM. Partly because EM's stint at 126 has been quite inconsistent. A struggle with In Jin Chi and Guty Espadas are evidences. Well at 130, it's a different story. Morales is probably in his fighting peak at this weight. It's just a wonder how MAB seems to always have a formula to beat Morales. Overall, he was brilliant when he was still champ at 130. EM by decision.