I tend to fly a lot of ORD-MSY on the evening flight (8 PM Departure) and I can tell you that the aircraft has varied from a 737 to a A319 a lot. For some of the earlier UX flights they've moved to the EMB170 which is really nice over a CRJ.

Unfortunately, at the late departure, no there is no meal service on UA.

I'm surprised your check in experience wasn't perfect at UA. I've found MSY to have some of the best check in agents especially at night when there are no lines at all at UA.

And obviously, some days are better than others and some days are worse than others. The AA flight isn't always going to be delayed and sometimes you'll get aircraft with more IFE.