That may be the problem. Flying 50,000 miles a year, spread over five airlines, won't get you anything with any of them. Put all those miles on one airline, they'll like you a lot, and will show it with things like the seat selection privileges that you don't get now.

So, FOCUS. Pick the airline that meets your needs best most of the time and try, all things being close to equal, to do as much of your flying as possible with that airline (or its alliance partners). Each airline has its forum on FT. They may help you pick one. They will surely help you maximize your frequent flyer benefits with it once you do.

(And, by the way: welcome to FT!)