United Airlines is among the largest airlines in the U.S. and the world. It’s the dominant carrier at O’Hare International in Chicago, and it operates domestic hubs in Houston, Newark, Denver, San Francisco, Washington-Dulles, Los Angeles and Guam.
If your home airport is a United stronghold, or if you just choose to fly the carrier regularly, you’ll want to check out the airline’s frequent-flyer program, MileagePlus.