I like AA out of Denver. The AA employee whether at the ticketing desk, the gate or the AC are all well above average. My upgrades always clear.

Depending on where you're traveling to, its not that much difference in terms of time. DEN-LGA is scheduled for an 1:15 longer on AA than UA but I'm always in F so I'm more productive or rested. The connection in ORD doesn't add any miles though as its the same distance from DEN-LGA as it is from DEN-ORD-LGA. Great service in the AC and they're very proactive in terms of flight disruptions.

Plus, UA is cutting back in Denver.

Then again, its a matter of your travel pattern. If you are going to Kalispell or Idaho Falls, AA's not going to get you there.