Lately, I've flown a lot of AM doing JFK-MEX-UIO, JFK-MEX-SAP, IAD-MEX-BOG journeys all in Y and what I've found is that with AM, the customer has to research the aircraft type in advance.
JFK-MEX on the 788 or 789 is truly a pleasure to fly, and on the 7S8 is perfectly okay
MEX-SAP for 2+ hours on an E170 was murder
MEX-UIO redeye (dep 1:30 AM, arr 7:00 AM, flight time less than 4 hrs) was murder on an old 738 with USA registration
IAD-MEX was disgraceful on an old leased 737-700 with Ireland registration
MEX-BOG-MEX was a pleasurable flight on brand new (new plane smell) 7S8.
One crazy flight that AM runs is the JFK to Monterrey flight which is 5+ hours on a E170. Crazy, but my friend from MTY said he'd pay a lot extra for the nonstop even on a regional jet than connect at MEX, IAH, or DFW