Windows 7 Ultimate for me. I still kept it as a boot option on my main PC until about a year ago because I thought I still needed it for a couple windows apps and games.
I tried Win8 at one point and hated the changes. I also tried Win10 and one of those “forced bloody updates” bricked my machine so I said ‘fuck that’ for good.
I’ve dabbled in Linux for 20 years, and run Ubuntu on my living room HTPC for at least a dozen. My main PC runs EndeavourOS now and even gaming has been pretty great.