Originally Posted by
honu
Yes, of course. Also keep in mind that some discounted *A economy fares only qualify for 50% mileage credit on US, whereas you can still get 100% on UA/CO (I'm thinking about SA, LH, but there may be others). IIRC, this is a fairly recent change. Considering that UA/CO allow one-way awards and US does not, I'd say that lately the US advantage has diminished.
However, conversely more fares flown on US metal qualify for full mileage credit on partner programs than UA/CO. Take my favourite *A program Aegean for example, all US flights count as 100% mileage, but most discounted UA/CO fares only offer 50%.
UA do offer one-way awards, but no stopover on those.