ORD is two separate airports to me. I enjoyed it as an AA regular about 15 years ago. I hated it as a UA regular 5-10 years ago. I don't fly through there as often today, but I still prefer the AA concourses over the UA ones.

Terminal C in particular was always so swamped with people that I could hardly ever find a seat at a bar/restaurant when I wanted something better than fast food.

We were asked if Atlantans like Delta and so I gave my opinion: it's a junk airline with the worst FF program in the US. If you fly twice a year and only care about direct flights, it's great for you; If you fly a lot, it's the least-desirable choice of the big 3. Delta's SkyPesos are worth less than the others and the SkyTeam alliance is easily the least-valuable alliance there is, with respect to quality of partners