Windows 7 (and Vista updated to the latest service pack for the most part) is a step in the right direction. Better than the lumbering, slow monstrosity that was the original release of Vista. Windows 7 is also the first release of Windows that actually sometimes gets faster on hardware that was previously running XP.
I don't like Windows in general because of experiences I've had with various versions in the past, and lots of wasted time cleaning up malware on clueless users' boxes. The whole Microsoft monopoly thing used to be a factor but to be honest I really just do not care anymore; it's an empire built on selling crap not worth its price, but there are lots of companies that do that (look at most Sony products, some current Nintendo products, and some Apple products for more examples. Or Ford, or HP, or ... )
I would have to say that XP is my all time favorite. I have 7 now, but XP was my best friend. Going from Windows 2000 to XP was a huge leap for me... even though the structure was the same, the UI update was so awesome to me at the time. And I loved the Bliss desktop wallpaper. I used it for almost 3 years just because it reminded me of a place I went to often when we lived in Puerto Rico.
I never even had Windows Vista. I used it from time to time on my Dad's tablet PC, but it didn't impress me. Windows 7 is great and I love using it now. I don't think I would go back to XP, even though I do like XP more.