Pilot is the only one I will buy as WHS without flicking through the contents first and generally, on average, provides more material of interest. Today's Pilot does have some great stuff occasionally as does Flying, but without those individual great articles I often find little of interest.
I will buy a copy of Flyer at when Gatwick or some such, but what looks like a set of great articles usually becomes a boring and turgid read and I can't put my finger on why exactly.