If your concern is INTL upgrades, US is out since they don't fly to Asia, *A upgrade program requires Y/B fare which you might as well paid for discount Z ticket. CO is merging with UA so basically down to UA.

Your choice seems pretty simple to me

Seriously, sign up both CO and UA, then sign up each of their credit card and get their sign up bonus. At the end of the year, both programs will merge so you get twice the sign up bonus.

One redeeming quality with US is they have some ridiculous miles purchase promotions which you can purchase enough miles for a biz award ticket for < $2000. Don't know how long this party will last though.