When I read your post I just knew that you were going to say Chicago! Of all routes in the network out of London, American in London gets most complaints about the Intl ORD base. I do not know what their problem is.They are so hoity-toity some of them that they really appear not to know nor care what treatment they give to passengers. on one memorable occasion on AA90 to LHR, the sourpuss that we were saddled with just got to much to bear, so we moved over the other side (The lamented MD11 was only a third full so we could), on the other side of the plane the very senior FAs were just delightful, and in great contrast to their younger colleague. I wish that she had asked me why I had moved as I would have told her.
Equally memorable was one AA41 (I think ) that from the moment of boarding I knew was different. The Fas smiled and bounced around the cabin - the reason soon became plain, this flight was manned by MIA crew. Oh the difference. Other crew bases that attract a lot of complaints are LAX and SFO for HNLs and SJC.
Complain loudly. It is simply not good enough.