I feel Vista was by far the best. 7 simplified it a bit, but that Start orb and black taskbar on Vista, man, that was glorious.

That's a matter of taste, but for many it was the Windows they used first and/or spend the most time on and there's a lot of love for that reason alone. I never used XP all that much, but I always changed the theme to the Windows 2000 look. I really didn't like the default, it looked unprofessional and clunky in my eyes. Upon release XP was also pretty universally mocked as a Fisher Price-like UI.

To me Windows 95/NT 4 is still the gold standard in Windows UI. It's certainly not the prettiest, that would be Windows 2000, but it was easy to use, easy to navigate and efficient with space.

I found each of 2000, XP, and 7 to be excellent in its own unique way. I'd be happy with any of them. But it also felt exciting to upgrade.

It's all been downhill from there as far as UX goes.

Perhaps with the Zune theme installed.

You mean 7 ;)