The average Joe does not care much about the open source philosophy. If it's free and works well out of the box without having to touch the command line, they would be happy. This is where I think Linux mint wins even though it includes many proprietary codecs.
It looks and works like Windows 7 and most people would feel comfortable using it.
For old computer hardware choose the lightweight Mate edition of Linux mint.
Ubuntu had its break through when it was the first one to get things to be more standard. Now with Systemd and easy build systems https://build.opensuse.org/ just about anyone can get a basic computer going quickly and easily. I still think Windows is the hardest and longest OS to install.
But they have gotten way better, too. The last Windows that I regularly used was XP, and I remember it being a pain in the ass to set up (on the scale of "I'll dedicate the whole weekend to getting the OS and drivers installed").
Just recently, though, I set up a dual-boot on my desktop PC, with Arch Linux as default, and Windows 10 for the few games in my Steam library that are not Linux-compatible. I explicitly chose Windows 10 for enabling my DirectX-12-compatible card.
The setup process was surprisingly straightforward and despite the very new hardware, it found all drivers out of the box and everything went smoothly. The only annoyance is the gazillion spying features that you have to disable, and the other gazillion spying features that you cannot disable. But since I'm only playing games on that OS, and the other OS with all personal data is on an encrypted disk, I don't care anyway.
A reasonable response: http://www.zdnet.com/article/no-microsoft-is-not-spying-on-y...