I switched to CO directly from NW to avoid getting sucked into SkyPiles although more than I would like of my formerly valuable NW Worldperks miles did. I have been pleased with CO, and to my surprize have had 100% upgrades on my domestic legs in aircraft with 2-class cabins so far. CO is not NW, but it beats the stuffings out of DL.

My latest comparative expenience between the two airlines was last night. I needed an award ticket for a relative to travel over here (TATL) in shoulder season with some leeway on outbound but none on the return. Trying to get rid of my remaining SkyPiles (former WP miles), I first called DL. They found nothing on the precise dates but offered an option with an overnight layover enroute on the return and a different date on the outbound for *ONLY* 150K miles in Y. I said ''no thanks'', called CO and got the exact dates we wanted for 55K miles. DL is an absolute horror story on redemptions and I will never again buy a revenue ticket on DL for that reason.