Wow
WOW . . this is the easiest question I have heard lately.
US/CO & Star Alliance . . . hands down.
Redemption is far superior in terms of availability and value in Mileage Plus v. SkyPesos. I fly to Asia often and 65K gets me where I need to go on MP and that is usually onboard an SQ flight.
Long time elite in both programs and likely MM ion both with a few years. Given the choice I fly UA/CO because of the FF program benefits.