Wirelessly posted (BlackBerry9630/5.0.0.591 Profile/MIDP-2.1 Configuration/CLDC-1.1 VendorID/105)

The short of it is that if you are flying both carriers then you should link your accounts and use the account of the metal you are flying on each time. The choice of earning the CR1s and SWUs on CO or UA is relatively trivial and for most folks I think the correct answer is UA, but no matter what you should link the accounts and get the match if you are flying on both carriers. A UA 1P has higher upgrade priority on UA metal than a CO Platinum. That matters. And they are combining the earnings on the back end in near real-time for earning this year so you don't have to worry about that part. It is actually very much in favor of the passenger in just about every way I can think of.