IMHO of course:
Pilot - Was once the leader, now only good for a laugh at what the magazine 'experts' write. Aerohack, please come back and show them how..... The recent 'How to' on short landings was a classic!
Flight International - Best read from back to front
Today's Pilot - Was a bit of a spotters mag to start, but this months issue was excellent. A very good profile of Nigel Lamb, a good flight test of a Lake Buccaneer derivative, and some good classifieds. A fair mix of everything GA, and readable.
Flyer - Not bad, definately taken over from Pilot as THE GA mag.
Popular Flying - Ok if you like plastic aeroplanes and adverts.
The AOPA magazine is promising, but looks so much like Pilot magazine did just before it was sold to the Archant Group, that I think I AM reading Pilot Magazine!
As with everything, everyone will have different opinions. Best go and buy the lot and make your own mind up.
And I agree with Monocock, please stop inserting Transair catalogues with ever issue. If I want something from Transair, I know the number!
Talking of Popular Flying and Pilot, whatever happened to Peter Underhill? He of the flight tests dept....