Win7 on my desktop is my main one. I apply the policy that if something's not broken, it doesn't need fixing. Even if the next 'good' Windows doesn't use a lot more resources, it'd still be noticeable. My PC might last me a very long time given I don't really play new games though.
I have Win10 on my laptop and haven't died. I use it for work and reading Facebook or posting/editing photos when I'm away, and it's been fine.