Leeds
As a regular flyer, I am in the fortunate position of being within 90 mins of Leeds/Bradford, Doncaster, Humberside, Manchester, East Mids and even Birmingham. I book my flights according to price and generally have no brand loyalty. However, in the case of Leeds, the problem for me is access to the airport. It's either a fast, albeit longer run via the A1 and A658 or the shorter, but slower run via Leeds or the Leeds ringroad. Compare that to East Midlands or Birmingham, and it is easy to see why so many South Yorkshire folk head for those airports. A rail link would probably help.