Uhm, I use AD&D 2nd, 3.5 and 4th edition.
My older brother is old-fashioned, so he uses the good old 2nd edition rules in his campaign, and up until recently I had a 3.5 campaign running (but I guess it's over, and I'll probably never play another 3.5 game again). Not long ago, me and my friends started playing 4th edition, which my brother has boycotted and in which I'll be starting a campaign soon.