Well, I had some experience with Pre-Windows GEOS. Anyone remember that one?
So, when I got my very first PC, it came with Windows 3.1. When Windows 95 came out, I was in line at midnight to get one of the first copies and also bought the first official 'made for Windows 95' game: Sierra's "Outpost".
I did the same when Windows 98 was released as far as getting in line to get a copy at midnight.
But, I let XP slide for quite sometime due to the activation scheme.
However, after getting SP2, XP seems to be the best experience with Windows so far.
So, XP gets my vote.