another thing to consider: NW has earned international FC upgrades, and partnerships with AS; CO partners with HP (well, so far).

FWIW I chose CO's program even though I live in a NW fortress hub. most of the three or so CO agents at DTW know me by now , most sales out of a fortress hub are almost never on the dominant airline, coupons are not reduced in strength, etc. Maybe I'm just a sucker for a texas accent on the phone.