AD&D 1e/2e. And contrary to what the meme says, I've also played later editions, Call of Cthulhu, Weird Frontiers, Traveller, Mothership, Dungeon Crawl Classics, Mutant Crawl Classics, Teenage Mutant Ninja Turtles, Symbaroum, Dolmenwood, Troika, Don't Tell Mom & Dad, and Toon. I'm probably leaving some out. Old-school AD&D is still my favorite.