My personal favorite may still be Moldvay Basic/Expert (mostly a nostalgia pick) . . . BUT, I voted 4e because a)it's the version I enjoy playing and running today, b) I don't want to play any other version, and c) I'm in two groups who are *rabidly* enjoying 4e.
Only on a single edition to single edition basis. I personally lump the 3.0, 3.5, and OGL/Pathfinder categories to compare edition preferences. That has been coming out to about 35% for 3.x to 45% for 4.0 for most of the poll duration so far (4e is gaining a little bit right now).