Barrera for me, he has been fighting at world class longer than Morales, and thus has met better overall opposition for a longer period of time; here is where I place them in Mexico's all-time list:

10 Erik Morales
9 Vicente Saldivar
8 Lupe Pintor
7 Salvador Sanchez
6 Marco Antonio Barrera
5 Jose Napoles (Adopted Mexico as his own country; Cuban by birth)
4 Ricardo Lopez
3 Ruben Olivares
2 Carlos Zarate
1 Julio Cesar Chavez

Mentions to: Humberto Gonzales, Miguel Canto, Rodolfo Martinez, Alfonso Zamora, Daniel Zaragoza, Joe Rivers, Baby Arizmendi, Chalky Wright, Manuel Medina, Rafael Limon, Jose Luis Ramirez and Jose Luis Castillo.