The first game to open my mind to GMless play, and how lucky I am that it was. The Belonging Outside Belonging system has launched a thousand RPG ships for good reason; these games simply work. And there's two of them! Heartbreaking queer apocalypse AND the passionate yearnings of the Jewish shtetl? Truly, what more could you ask for?
These are nearly always my first recommendations for folks who want to try GM-less/GM-ful play for the first time, and I don't imagine that changing anytime soon.