Consensus usually has Chavez as the Mexican GOAT, and in second place many have either Olivares, Sanchez, or Saldivar. But let's just deal with Olivares vs Sanchez in this one. I think greater is up for debate, and I can entertain Olivares having the edge. Better I say Sal. Sal wasn't as dynamic an offensive force, but he was more complete, with less holes, and a helluva lot more durable. If we're measuring greatness, Sal also has the bigger wins.
Olivares is greater overall, I reckon. He'd probably be no. 2 on my all-time list of Mexicans and has an argument for no. 1 as well. At their respective peaks (1969 for Olivares, 1981/82 for Sanchez) they were both bloody amazing. I'm comfortable picking either one but might just lean towards Sanchez for the same reasons as X.