In any surveys it does very much depend on how the result is gained. I would give more credability to BT survey as it is readers survey which involves completing online or paper form and posting.
I don’t take the other magazines Airpocket mentions so I can’t comment on how they gather the awards, but if they are decided by a “panel of experts” then they certainly won’t float my boat! I know from an award given in transport that out of the six elements that make up the criteria only one is customer focus, the rest are irrelevant to the customer and therefore an award could be given to a company that has say the right environmental policy but has a poor customer record.
I do feel that in asking for the “worst” in any survey it does open the door to saying say Ryanair for customer service even though the responder has never travelled with them.