I flew MTY-CUN with a stop in MEX last year on Mexicana, MTY-MEX was a F100, but flight MEX-CUN was on a A320, It was delayed 4 hours because mechanical problems, and they didn't do anything, but keep us walking during 3 hours telling us different gates, (ie. from 9 to 13, from 13 to 3, etc.) they didn't let us take another flight (AM or MX) nor being stand-by passengers, and they even didn't gave us a coke. I was kinda disappointed of their service which is usually good. Return flights were awesome, CUN-MEX on a 757, best flight and service I ever got, and MEX-MTY on a F100, a good flight.
Both are good, AM is more like for business people, and MX for tourists.