Go with Pop! Pop! Is a great OS and has pretty much everything working right out of the box. Go with Gnome so that people understand they need to do things slightly different rather than trying to use a Linux machine like a Windows machine. Plus Gnome is just awesome. Hit the windows key, type the first couple letters of the program you want to open, hit enter, done! The Pop shop has almost everything an average user would need, so you can install things with the click of a button without having to search the Internet, and updates are a hands off affair.

Edit: since you're not a Linux user I'll clarify Gnome. Gnome is a desktop environment, and Pop is the actual operating system. In Linux you can change how your computer interface looks and works by choosing different desktop environments(DE). A variation of Gnome is the default DE for Pop, and it works great. KDE would be the DE most similar to Windows, but it has enough differences that it can frustrate Windows users. Gnome is completely different, so they'll take the time to figure something out rather than just getting frustrated that it's different. Besides, the learning curve on Gnome is basically zero. Just use the Windows key and start typing. It's literally that simple.