I have flown AeroMexico on Delta codeshares many times, in both coach and first, and the service has always been very good to excellent. They are very punctual (much more so than U.S. carriers), and in-flight service is better than Delta in some areas, and not quite as good in others. In first, food is usually better on Delta, AeroMexico doesn't have audio on most of their planes, but AeroMexico's seats are much better than Delta's. I have never had any problem with the skill or attitude of AeroMexico's flight attendants, although they tend to be more reserved than Delta's. AM offers newspapers (something I wish Delta would do) and has two excellent magazines. On a few occasions, boarding at LAX has been a bit more chaotic on AM than DL. At DFW, ATL, and MEX boarding is very smooth.

Yes, segment upgrades are used exactly as they are on Delta U.S. flights. All fares except L, etc.