I could see staying with Windows 7. That was the best version Microsoft ever made. Microsoft finally figured out how to make it stable, and it didn't have all the ad and cloud crap nailed in. You can run current Firefox, current Thunderbird, and current LibreOffice, which covers the basics. Most Windows software still works.
Then Windows 8 came along and decided flat squares were the only option anybody could use, removing theme transparency support altogether.