Originally Posted by
sdsearch
I slightly disagree with the recommendation above to sign up for them all.
Next, you need consider that some are dupilcates. For example, no need to sign up for both UA and CO and US. For that group, sing up for CO (because it's your CO-type number which will become your UA number once CO/UA finish merging), and use it for all CO, UA, and US flights.
I disagree with this. While UA/CO and US are both *A, their programs are much much different.
UA/CO is a partner of Chase Ultimate Rewards, so if you earn Chase UR points (from the Sapphire Preferred or Ink Bold), you can transfer to UA/CO. They allow for one-way awards.
US is not a partner of anything except SPG. However, they have a lot of "buy miles" promotions and you can gain a lot of US miles through promotions. US does not allow for one-way awards. In addition, their Barclay's credit card is one of the best deals of credit cards I think -- the credit inquiry is done on Transunion instead of the other 2, 40K miles are earned on first purchase, and you get 10K miles each year (which washes out the $89 annual fee).
Sure, both can be used for *A, but they are completely different programs. I participate in both and am glad I do. OP has said that they don't fly enough to earn a lot of miles, so elite status isn't an issue. If OP were to buy a ticket on *A, he could decide later which airline to credit to. But should still sign up for both programs.