When I last flew from Raleigh to O'Hare, I took an American Eagle flight. Today I took a full-blooded American Airlines flight. AMR owns both airlines, and they both operate out of the same concourse (and the same gates sometimes) at both airports.
Heavens, but the two airlines have differences.
First, most obviously, American Eagle doesn't fly anything larger than the 70-seat Bombardier CRJ-700, while American doesn't fly anything smaller than the 140-seat Boeing MD-80 (which they are phasing out in favor of their newer Boeing 737-800 planes. This makes sense, as Eagle flies short routes to small cities and American flies all over the world.
Second, less obviously, American has a fleet of baggage trucks at O'Hare, while American Eagle apparently has one rickety bamboo cart pulled by a 20-year-old mule. Evidence? The last four times I flew in on Eagle, I waited 40 to 45 minutes for my checked bag. Today, flying in on American, in the 12 minutes it took to walk from the gate to the baggage claim, my bag had gotten to the carousel.
Seriously, Eagle? It's time to retire Francis and combine baggage teams with your parent airline.
 K19, the farthest gate possible in American's terminal, a gate so far from baggage claim they have Sherpas to guide passengers, and still two AUs closer than the C-concourse is from United's baggage claim on the other side of the airport.