I used to use windows 7 until I got a new laptop. In my opinion, windows 7 is a bit outdated now, it's like using windows XP back when windows 7 was still the big thing.
Currently I use Windows 8.1 and I've grown to like it. I do use Windows 10 nearly every day at school and in my opinion, I'm not much a fan of the work-flow on that operating system (and the updates ffs)
With me, windows 8.1 is the perfect mix between 10 and 7 and I just really like it. I know one day I'll upgrade to windows 10 though, but I may not due to possible compatibility issues with old pc games (like pre 2010 or older), since I play quite a lot of those lmao