You're asking this question in the Delta forum, where (most) of us are DL loyalists.

I've flown all those airlines to MEX, except AA. I think DL is definitely the best product across the board. The one exception might be if you catch the Dreamliner out of JFK on AM, which is a really comfortable nice ride. If you're in F, service and food on AM is not going to be the same level as DL, but close.

As to pricing the flight, you will likely find the same price on either AM or DL, regardless of which carrier is operating the flight. It makes most sense to buy the flight on from DL because there won't be any issues then with handling IROPS or other problems. Though theoretically, it shouldn't matter, sometimes it can.