As a kid I grew up with a XP computer. Loved Vista but 7 was good to. Originally Windows 10 was rocky but eventually became the amazing OS it is today. Lately I have been using Chrome OS I would use it for everything if there was Steam support.
I use both MacOS and Windows, and althought lastest versons of OS X are introducing some useless stuff for me (siri, for example), I found this OS very fast, stable and secure, it has never give me any problem.
Windows 7, as it runs well with all software, recent or old, thus providing excellent compatibility with it with no OS bugs or restrictions and to point out its accesibility to run very well even on weak or not so new computers. Perfect OS in my opinion thanks to its flexibility.