going to Europe I think that AA is the best program for you. Great route system and you can upgrade from any fare.
I Asia is your most likely travel then UA might be best as there route system is better to Asia for upgrading, but they do limit you to H fare or better for upgrade, except for SWU use.
CO might be it for domestic only travel with great mile earning capability and free upgrades. No one seems happy with their International upgrade rules though. i.e. HoKeY Fares.
If upgrading is your thing then AA might be the ticket for you. I live in DFW so it is a slam dunk for me. Good luck on your choice.
dallasflyer