Funny, I needed to fly back into PDX a few weeks ago from the east coast and so found a great DL -up fare. I was on a decrepit 757, with about a 12"x18" piece of plastic missing near my feet, so I could see into the fuselage. They plugged it with a pillow and blanket ;-) and told me it wasn't keeping us from flying!
I think it is so route/plane specific. I mix pretty evenly between DL, AA and AS metal, often in F and have had bad/good/excellent on all of them. Rating any one of them on a single segment is going to be a bit misleading.