"Which is better" depends on the route, aircraft used, crew attitudes, and service (i.e. food) provided. However, I am flying both DL and NW this year as an elite on each and I like them both in F. I have noticed that on some comparable routes that DL will serve a small meal they call a snack and NW will serve a snack basket. DL also has IFE (TV shorts) even on shorter flights. However, the legroom on the DL MD-88 leaves a lot to be desired, while the legroom on the NW Airbus flights is very good. So I think it is relative. However, both are better than coach on either!
