Only have perhaps a half dozen DE razors, but if I had to pare it down to just one I would keep my 1959 Gillette "FatBoy". And, to take this a step further, if I had to choose just one of my two dozen or so shaving brushes and soaps/creams/croaps, it would be my custom Shavemac Model 177 Two-Band Silvertip Badger Hair Brush and Arko soap, respectively.
Tim
Tim