LanFan's comments were 110% inaccurate. AMX and MXC are jointly owned by their parent company, CINTRA. As of now, there are now plans for the two to be merged, but the current ownership will be divested.
Aeromexicos fleet consists of DC930s, MD82/3/7/8s, 757-200, 767-200/300. The Mexicana fleet contains the F100, 727-200Adv, A320-200, and 757-200. Currently, the two airlines are helping each other, and sharing costs, code sharing, overall trying to save money. Historically, AMX has been the more 'service oriented' international carrier, but Mexicana has recently been expanding internationally as well. Domestic service on both airlines is as good or better than US airlines. On almost all flights, regardless of timne or flight duration, a meal is served. International service is top notch. A joint fleet purchasing plan may go into effect later this year, speciffically in regard to the 717/737NG, or A319/A320. Basically, youll get the same service pretty much on either airline.