I favour Haraka's suggestion of a poll of existing readers, because each of us can only indicate our own, often highly individual areas of interest based on our life experiences to date. Trying to extrapolate from personal preferences to predict trends in popularity amongst others is a hopeless exercise, the sample size would be far too small and easily skewed.
Speaking only for myself, my lifespan encompasses the aviation eras of keenest interest to me, with emphasis on WW2, the Cold War period, and the proliferation of excellent aviation museums and warbird-centered airshows in recent years. The early years from around 1910 to 1930 are of less intense interest to me, and straight away that probably gets a reaction from others whose tastes differ markedly from mine.
My enthusiasms are strongly influenced by personal experiences. WW2 is an obvious starting factor, I have memories dating back to 1942 or so, when my home was overflown by a wide variety of RAF (and Luftwaffe!) aircraft. Then as a member of the RAF section of my Grammar school CCF, I attended all the annual camps at active RAF stations (Driffield, Andover, Hawarden, Waddington), where I encountered Meteors, Chipmunks, Ansons, Vampires, Canberras and the mighty Vulcans of 230 OCU. I enjoyed air experience flights in some of these, and have a vivid memory of a half hour trip in a Canberra T4 when the kind pilot let me have the controls for a while. Then there was the week's gliding course at Halton, where I went solo for the first time. Not surprisingly, any articles and photospreads of any of these will virtually guarantee my purchase of the relevant magazine! But I am not a typical reader perhaps, so I feel that a wide-reaching poll of reader's own interests is a very worthwhile exercise.