Windows 7, 10, or 11. There have been some feature regressions from 7 to 10 and from 10 to 11, unfortunately--I don't know what the heck Microsoft is thinking--but there have also been some additions/improvements with those successive versions, too. So it's hard to choose. But I currently run 11 because it's compatible with the most apps (and I don't think 7 is even supported anymore regarding updates) and has a few important features like the ability to run mobile apps (though I don't actually use that feature because I haven't seen any good apps in the mobile app store ;P) and the search function in the task manager.