My advice, for whatever it's worth, is that if you are running Windows 8 or 8.1, you should go ahead and update. 10 fixes many of the issues that people have with 8, and it will be supported for longer.
As for upgrading from 7, I used to recommend it, but I've changed my mind on that one. The way Microsoft is being extremely pushy about the update is a huge turnoff, and I don't want to support that behavior. If you are running 7, and you are happy with it, then stick with it. Just keep in mind the end of support date for Windows 7 (January 14, 2020) and make sure you migrate from it to something else before then. You still have 3 and a half years, so it's not yet urgent, but it is something you should have in mind.
(On a related token, no machine running XP should be connected to the internet at all, and if you have one you can be certain that it is compromised. Windows Vista support ends in about a year on April 11, 2017, so it is getting to the urgent stage to replace if you are still running that)