Sounds like you're the one who's biased. United doesn't give complimentary upgrades to GS members, and it's supported upgrade system has allowed me to upgrade 90% of my flights this year. The CR-1s and 500s I earn from my international trips has given me more then enough upgrades to use on my domestic flying. With two west-coast UA hubs, the OP would be much better off going with United. Especially if he does any international flying at all - much easier to upgrade internationally on United then CO.
Originally Posted by
thegeneral
Please also keep in mind that UA and AA really don't value their domestic travllers a lot. Both upgrade you very little. AA has an automatic program similar to NW, but only if you're platinum. UA will upgrade its global services and then mostly sell their upgrades. You'll get upgrade certs for them, but you often won't be able to use them on the flights you want.