Technically either OS would work fine and both approaches have easy install methods with my Windows Installer and Paul P's octoprint_deploy script for linux. The biggest difference is that a ubuntu server OS for example would consume far less resources just for the operating system and you wouldn't have to worry about failed prints due to windows update restarts.
I have had good success with these mini PCs.. Plenty of power and they come with the OS of choice installed. Just run Paul P's script and you should be good to go. Bonus is that they are under $100.. Just!