I loved windows xp when I first started using that. Windows 7 is also great but you need much better hardware (compared to XP) to use it properly.
I have to say Windows 7, even though XP was the best OS for more than 9 years since i've used Windows 7 for the past year I have to say it is just great in performance it does everything XP does but better. VIsta was just a born failure in my eyes.
OS X is the best windowing system... Go Mac and never look back I've used every version of Microsoft's poor attempt at a graphical interface since version 2 and wow was that ugly. There is no doubt that with Windows 7, Microsoft finally got things right. Everything before that is crap even leaving aside utter failures like the Millennium edition.
I was a firm "Mac-guy" until Windows 7 was released...for a brief period it convinced me to drop Mac OS completely and turn to Windows.