Currently have an AD&D 2E game and a D&D 4E game going.
The D&D 4E group is finishing tonight, and I have to say--good riddance. You need to have the D&D Insider subscription to use the online tools in order to keep up with everything, and the tools available to your character just get stupidly complicated at higher levels. At 26th level I have 22 powers or some insane number like that. It's entirely too WoW-like and I doubt I'll ever be playing 4E again.
Historically I've also played Traveller (classic traveller) and D&D 3.5. Of all the D&D rulesets I liked 3.5 the most--I felt it was the best combination of choices and ease of use, without the repetitiveness of 2E or the insanity of 4E.
I'd like to try Pathfinder at some point, but don't think I'd be good at DMing and haven't found an existing group.