I voted 3.1 also. I have a lot of good memories of computers in that era. Lots of bad memories too actually. In any case, when I'm on a windows box, I still resort to using the command line all the time because it's what I grew up on.
On a side note, in many of the later versions of windows program manager (progman) is still present and can be run. What this essentially does is give you the windows 3.1 interface on top of your later version of windows. I don't know if it was present in me, 2k or xp, and I highly doubt it's in vista or 7, but I know for a fact it was in 95, 98, and 98SE.