I use primarily WIN 7. I refuse to upgrade to Win 8...will wait for the next incarnation of windows that will be out soon. Be that Ble, Windows 9, Windows 10, whatever they want to call it.

Windows 7 but maybe i will move to Linux in future

I was on Windows 7 RC's long time, time was passing by and now I moved to Windows 8.1 and everything is working very well for me. I don't have incompatibilities at all on it like I heard a lot o peoples complain.

Windows 8.1 x64 and Windows7 x64.
Windows7 is best.

Windows 7

staying with win7 until win10 comes out.

Windows 7 is still my weapon of choice. I however have switched to OSX on another notebook and have to say I'm less impressed with the system stability than I thought. It randomly crashes and sometimes does not wake from the standby mode.

Windows 7 ultimate.

I use XP on my main computer winch is a desktop. Intel 4 cpu 3.4 ghz. Works Great!
For watching on my LCD 46" TV I use my HP laptop about 3 years old with windows 7. Also work great since I replaced hard drive with a hybrid 1 terabyte drive.
2 other computers also work great. 1 more XP that my wife uses and 1 more laptop with widows 7. I am a happy camper with my computers:=)

I use a macbook pro, a synology NAS & for watching movies, a Raspberry