Originally Posted by Eastbay1K

I've flown SFO/MEX/EZE many times on AM, although it has been a while.

Pluses:
It is really the most direct routing.
If you get a 789 MEX/EZE, it is a quite comfortable ride. Can't say that for the 788 (which is ok at 2-2-2, but not great). 789 has a self-service bar / snack area set up.
DL lounge @ LAX is very nice.

Neutral - F&B and inflight service is meh to decent, so it may be a wash between UA and AM. AM has seatback IFE even on the narrow-bodies, and the seats are more comfortable than UA's narrowbody seats.

Minuses:
MEX has no sterile transit. Everyone goes through immigration and customs. Fortunately, bags are now checked thru. (You used to have to wait for bags and re-drop). Then you go up through security back to the departure area. This process can take between 20 and 90+ minutes, unpredictably so.
AM lounges @ MEX are overcrowded noisy messes. Some people love them. I'm not "some people." The AX lounge, if you have access, is better. But there is typically a line.
MEX is an overcrowded, delay-prone dump.
AM is an unethical piece of caca business operation. If there aren't any IROPS, you may actually find the experience not unpleasant. If anything goes wrong, make sure your preferred deity is on speed dial.