Midwest Express, hands down. First-class seats and service for the same fare you'll pay on other airlines! Although their route network is smaller than the majors, they serve almost all major US cities via MKE, OMA, MCI and IND.
If you can't fly them, fly Southwest. Although the service is minimal (but the tix are cheap!!!
), their planes are clean and reliable and their people are really friendly and a lot of fun to fly with! I've never had a bad flight on either of these airlines, and both treat you like a human being, a rarity in the US airline industry!
Enjoy your trip!