I really like Chrome / Chromium OS, though I'll be sticking to Windows 10 for the foreseeable future unless major game releases start getting ported over (though the chances of that happening are basically none).

I was fully on board the Microsoft train with W7.  I remember telling everyone who was distrustful after Vista that W7 was the real thing.

Then W10 came out and the frustrations and negatives kept mounting.  Now I want as little to do with the "Windows 10 ecosystem" as possible.  I don't even want an Xbox any longer--not because of "Xbox" but because I have zero trust for Microsoft.  

Honestly, I'd switch to Linux Mint in a heartbeat if it wasn't for gaming.  I've dual-installed Mint a few times and I like it.  It's much more user-friendly for someone who has always used Windows and I enjoyed it more than Ubuntu.  

macOS, followed by Windows 10

Windows 98 SE was the best Windows, followed by 7

Also really liked BeOS, too bad it died down. But with Haiku at least some spiritual sucessor is in the works.

Unless you use it on a secondary  retro PC, I wouldn't advise using XP anymore. Nowadays XP is a honeytrap for Virus and spam as it lacks almost any protection now.

Windows 10 by a mile for me .I just love it.
And yah... BeOS :) Was just soooo good...

Mac OS. All the way.

I def agree that Windows 10 has those security issues that stop it from being perfect, but it's not like I'm dying to have 7 back either, as great as an OS it was.

I guess Windows XP was the least miserable. This question is like asking what is your favorite tooth to be pulled out.

I'm sorry, I love Windows 10. I like it even more than 7. It's just some good solid software with an amazing minimalistic style.

An OS is just a means to get what you actually want so it's weird to have a "favorite". It's like asking "what's your favorite bus to work".

That said, whatever is the most up to date OS that lets me play the games I want.