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.