I use a bunch of different distros, mostly because I love to tinker and play. But if I am setting up for someone who is new, I go with either Ubuntu of Mint. They started out the same, but diverged pretty sharply, so there is a bit of difference, but either are very usable to someone starting out on Linux. To make it overly simple, if you prefer OS, you will find Ubuntu more familiar out of the box. If you are used to Windows, Mint's Cinnamon interface is more comfortable. (I personally like Cinnamon over Unity, but I stay out of religious arguments.) But both of them are easy to use and learn.