I kinda get obsessed with the game engines I run:
D100/BRP is my goto fantasy engine. Not just the actual % skill system, but also the Character ->Culture ->Proffession ->Magic System framework that originates from RuneQuest. RQ 3, in particular, introduced a whole framework of presenting setting information that I keep on coming back to.
OD&D. When I got back into D&D as a result of following the OSR blog sphere five years or so, of all the retro-clones Swords and Wizardry was a hit with me the most and I spun Crypts and Things off that (which is my Swords and Sorcery variant with a dash of Fighting Fantasy/White Dwarf 80s inspiration). It’s my gateway to stuff like the Black Hack and 13th Age. Should really graduate to running 5th Ed, but OD&D I can carry in my head. Also, Mitch’s Beyond D20 (which is what we are calling the system in Beyond Dread Portals) also builds a lot of modern narrative sensibilities on top of the S&W chassis, in an easy effortless way that doesn’t tax my poor aged sponge of a brain too much.
FATE won the narrative system wars of the 2000s that raged in my head sometime in the 2010s, swiftly dispatching HeroQuest to the dustbin of failed systems (although I’m feeling the urge to take it out and give it a spin again).
PbTA is still the hot new kewlness, that I’d love to write something for but I’m still at the learning through play stage with. But every game I’ve either played or run has been a hit with me.