I think I went: DOS 5.0, Win 3.11, Win 95, Win 98, Win 98SE, Win 2000, Win XP, Win 7 (my favorite so far).

Windows 2000 was one of my favorites once it started supporting games and essentially becoming just as much of a consumer OS as their other products. I always found it funny how much better it was than ME. My parents "upgraded" to ME (I think they just happened to buy a new computer for that short time it was out - what luck). I was soon able to get them upgraded to XP, thank goodness.