I've played 2nd, 3rd, 3.5, 4th and I'll throw in Pathfinder. In the past few years I've played other systems, most recently Savage Worlds. I've been writing up my own SW one-shot campaign which I call League of Extraordinaire Americans. The characters I use are Orville Wright, Annie Oakley, Harry Houdini, Nikola Tesla, and a young H.P. Lovecraft. Set in 1905, the adventure would start in Paris and then head to Istanbul and Wallachia.
Recently at one of our conventions' (MisCon) quarterly game days I played Dungeon Crawler Classics. I thought it was absolutely fantastic. The first one shot was with 5 players playing 0-level characters. My first got killed off 3 minutes in.
Another one I had played in recent years was the original Game of Thrones d20. I thought it was really good too, but the credit there has to go to our GM. The story he wove was amazingly intriguing.
Up until last week (moving this Thursday) I played in a game that used BASH. The storyline was good, I didn't care much for the system though.