If you fly mostly domestic, then CO is the way to go! Free upgrades, even at Silver. Depending on routes and times, upgrade chances can vary from 20% to 80%...I think 1/3 is about average, but higher if you stay away from EWR transcons anytime, and business routes on Mon. mornings or Fri. afternoons.

If you fly mainly international, AA is your best choice. No airline provides free intl. upgrades, but AA allows you to upgrade any published fare with miles. CO, a "Dr. Jeckyl" with domestic upgrades, turns into "Mr. Hyde" when it comes to their intl. upgrades. It's easier to get a seat on the Space Shuttle than to get an intl. upgrade on CO!

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