After many years as the USA's largest domestic carrier, United is now also a major world airline serving cities nationwide and throughout the globe, in conjunction with its partners in the world 'Star Alliance' of international airlines. United Mileage Plus awards are accrued on every United flight.
Delta serves major visitor destinations worldwide including Europe, Africa, Asia and North America, as well as a very extensive network within the US. With Delta you can earn SkyMiles on every flight. Delta is a member of the world SkyTeam alliance.
U.S. Airways offers extensive service throughout Eastern U.S. and a more limited service in the West. International destinations include major centers in Europe and the Caribbean.