Ubuntu was the first distro I was able to successfully deploy to non-tech members of my family, friends, and clients. For people who just wanted to browse the web, watch videos, etc and already had old hardware lying around, it was (and is) perfect.

(If someone wants cheap and simple nowadays, I recommend Chromebooks. But if they need free, as in I can re-use some of the flow of decommissioned machines from work, Ubuntu it is!)