I tended to upgrade almost instantly when a new OS appeared and I must say I had good experiences with all versions (never used Win2K at home) including ME which was the most performance wise on my 1997 Mitac portable that came originally with Win95.
But with Vista no. I hate Vista since the first beta came out. Too much resource hog, much useless applications, that Control Panel resembles like a f*** zoo!
I use Win XP Pro since day 1 and it is by far the best OS Microsoft ever made. Quick, very stable, highly configurable. Until a specific application that I need to use in a regular basis doesn't support XP, I will stick with it.
I'm on my third different full PC, since I bought my Win XP copy and I think this says everything.
Emulation wise it provided me till now the best experience, the Amiga coming in second place.