STL is a mix of DL & UA trips... but definitely more DL. Trips are not usually commutable on at least one end. Sometimes both ends are not commutable. Many of the crews live in STL. Ferry flights are more common as it is a maintenance base. Most trips are 4 days. DL overnights tend to be mostly east coast. The first leg is to LGA/JFK and then you won't get back to STL until the end of the trip.

ORD is mostly UA flying with an occasional DL trip. Many, if not most, trips are commutable. ORD crews are a little more laid-back. Most trips are 4 days. UA overnights are spread out all over. UA flying touches ORD and DEN a lot.

I can't say exactly what the average pairing credit is right now but it's pretty decent at every base.