IMHO, it depends on to where you most often travel from MCI and if you don't mind connections.

Southwest is the #1 carrier out of KC. Since Southwest doesn't have hubs, they call it a "major connection airport" or some such.

Heading to Newark, Houston, or Cleveland often? Go with CO or if you believe that the NW/CO partnership will last, stick with NW. Heading to DFW or ORD? AA will do nicely.

If you travel often and stick with an airline other than Southwest, you can easily get on a first-name basis with the airline staff.

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On the road, In the air,
I enjoy travel, From here to there.