Having finally got around to flying both recently, I can only boggle. I upgraded one sector on NW (with AS MVP cert) and the service was poor, the "meal" in 1st was a salad, there was no video and it took almost 45 mins for them to get the luggage off the plane! The sector in Y was 5 hours, yet they showed no video programming at all, gave out an uninteresting meal and had surly FA's.
CO's agents were friendly and helpful and FA's gave much better service. The meal in Y was tasty and there was a movie on the longer segment.
I would definitely agree with the comment that economy on CO is better than 1st on NW. I found NW horribly disappointing and CO quite good.
It's a shame that CO drags itself down by being allied with the likes of Northworst.