That would have to be the first Dungeon World session that we play on Twitch.tv. I had not anticipated on playing. The game, my fellow players and the system turned out to be a pleasant surprise. I have Dungeon World, but I was never able to grok the system. Playing it with an experienced GM showed me how it works, and that even inspired me to pitch it to my university friends instead of D&D.
Close runner-ups would be the introduction session of D&D that I ran for a family of four, and the same scenario I did for damanique, issue_i and a friend.