I have only viewed this at one remove, when seeing my mother through airports with wheelchair/buggy assistance. Or, when she first needed a walking stick, just getting to the lift and making sure that she had an aisle seat. She no longer travels by air but, in the UK, this was: IOM, LTN, LCY, LHR, BRS and in South Africa at JNB.
The best was JNB but in the UK it was pot-luck. Here I would agree with
TS and add that, in the UK, the kind of service you get is unpredictable. Since once can compare the airports run by BAAplc, once can see the enormous range of service offered. If LGW was great for you in May, it might be bad for you in June.
To drift slightly, but to explain why I think this: The same may be said of most services in the UK today. One branch of a shop may be good, another branch in another town, not so. You can never be sure what you are going to get - over the counter, at a lunch table, on the phone to customer services. Everyone has cut so far back that the cracks are now showing. I would say that there are very, very areas left when you can guarantee good service, reliable service, value for money service - every time.
To avoid Jet Blast territory
I would say that this is ALSO the case for the many airlines we use. Just because you have had good service for ten years, does not mean that the next five trips are going to be as good. It is the way of the western world.