Personally, I am comfortable working with Windows XP. Windows Vista and Windows 7 are also great for they have some advanced features.
i use windows xp because i have been using it since my childhood, so got used to it. it is also user's friendly unlike vista and window x-7. ?
Now i am using windows xp ,its working well but i will be upgrading to windows 7 as it has many new features,fast and reliable edition of microsoft windows
I have Windows 7 as my primary OS and Ubuntu on a second hardrive as I use it on my degree course sometimes. Linux is also usefull as the servers use it. The OS I currently have the least experience with is Apple which is shame as I'd love to do some application developing. Do you use any of the ultimate features..? I'm also running the 64bit on my desktop but don't see too much difference to the 32bit version on my laptop.