I prefer AA out of ORD (compared to ual) - just a smaller terminal area. Ual out of Ord is just too big, which means loads of expected walking post-security. It's similar at SFO. So that could be a consideration; a shorter walk at any airport is nicer. I fly out of ord 3-4 times a year, ever since 2005.

Overall I prefer VX the most but this doesn't answer the Topic.