I use Windows 7 Pro on my Desktop and Windows 8 Pro on my laptop. The laptop used to be XP Pro and upgrading to Windows 8 Pro only cost $40 when I did it. You should let us select more than one OS.
I use Win7 Ultimate SP1 now.And used to have Vista and Win XP Home Edition as it was easier to upgrade from Vista to Win7 a few years ago and still enjoy Win7 more than any other OS for stable and rarely find an error and i have a full file system storage on an External HD to rescue me in any time some bad thing happen.
As we have a new player in the os league I've edited the survey to suit. Many users will also be running dual boot and again this is reflected in the survey choices (you get 2).
I have been using Windows 8.1.1 but lately have switched to using Windows 10 Preview. Starting to get used to it and love it. I will not go as far as to say I will buy it in the final version. All depends on the cost.
There is no question, it's blatantly obvious, Windows 10 is less fuss to use; just clean, clear, relaxed & easy. "Less is more". Also, some ok new/added Features.
Interesting seeing what the Builds bring. New one today, BTW
Yes, I know, question only asks what OSs do you use. I use both. So pardon the wee unsolicited comment. lol
Windows 10 is being used the majority of the time by a wide margin! Not being shut off, just left running, too.