What OS are you most comfortable with?

I've used Windows since the days of Windows 98/xp, and Linux distros like Fedora, Ubuntu, and Mint. But if I had to choose just one for personal and professional use, it would be Windows. All things I want to use works.

Windows 7 was hands down the most comfortable one for me, and nothing else even comes close. I kept it for as long as I could.
 
For those that like windows 7/10, try out Windows 10 server. It's basically the stuff that was good in 7 and 10, but without all the extra crap. More customizable and easy to do zero telemetry. It does take some work to get some media stuff going, and until next update no bluetooth.