The site was mostly interesting in that some windows versions would beat others in unexpected ways.
It is subjective, of course.
It's definitely question-begging. When you're saying "best" you always have to follow that with "for what?" Gaming? Work? Letting mom check her email?
Windows 7 is undoubtedly more secure than WinXP. WinXP works with more software. And Windows 2000? About a year ago I installed Win2K in VMware and was blown away how incredibly responsive and quick it was in comparison to any other machine I owned, even inside of a Virtual Machine. I still don't understand why -- even with all the nifty user interface stuff turned off -- no other Windows even comes close.
Anyway, since so few programs here on the site don't work for it, I had to switch back to XP.