I did the UA Airbus 320 DTW-ORD thing a few months back (similar length, I believe) and was lucky enough to be in first. I got an OJ and a larger seat. In coach, I believe UA managed a full drink service, but it wasn't a full load. I guess it really just depends on how full the planes happen to be on any particular day. In general, mainline probably offers a more comfy experience, IMO.