The question is: Most often played RPG?
In recent times it’s D&D 5e, again, because I’m running that at the moment. In previous years there’s been all sorts of things and I’m not sure I could pick one in particular. I’ve played a lot of a lot of different games. I’ve also played in a sprawling modern day science-fiction-esque horrorific campaign known as ‘Glasgow’, that was stretched over several decades and incorporated many different systems including iirc the Fuzion RPG and the incredible Broken Rooms game back when it was known as The Nearside Project.
Also there was a heap of Call of Cthulhu, Space Opera, and Runequest. Couple of years of HERO System and Stars Without Number as well. That’s a lot of gaming…
I forgot to even mention all of the superhero games I played/ran with systems like Golden Heroes, V&V, MSH, DC Heroes, et al, not to mention my own homebrew supers game.
