Windows 7 if you are up dating.
My tech support said that we are waiting for Windows 9 or what ever they decide to call the next release of windows. He said they build hundred of machines per year and they have not loaded Windows 8 on one single machine. His opinion was that Windows 8 was designed for touch screen operation and when you used them on older screens you had problems. He also said that microsoft can not abandon all the xp user. In some instances you have xp machines running the government. And my CS 45 so XP will be around for a while yet. I'm still getting updates.
I have a dual operating system both xp and windows 7 I am almost all moved over to win 7.