When two things are so closely linked or attached that they act as if they were a single unit, they are united. Allied countries join together during war, united against a common enemy.

Delta consistently ranks higher than United in The Wall Street Journal's annual airline scorecards, particularly for reliability and overall customer satisfaction.

You can buy tickets without extra fees on united.com. To book with an agent, there's a $25 fee by phone, $10 at a City Ticket Office, and $50 at the airport. If you're an English speaker call 1-800-UNITED-1 (1-800-864-8331).

For all United Economy tickets, Premier Gold members can check two complimentary bags at 70 pounds (32 kg) each for travel between the U.S., Canada, Puerto Rico and the U.S. Virgin Islands. For travel to and from select international markets, Premier Gold members can check three complimentary bags at 70 pounds each.