linuxmemes

Complete agree: always mainstream distribution for new users - Fedora, opensuse tumbleweed, Ubuntu are all great choices.

There are a lot of distros that are great (for beginners and in general), but I recommended Ubuntu and only Ubuntu for two reasons:

1. It's the only distro other than SteamOS that Valve officially supports (and there's a reasonably decent chance folks wanting to try Linux are also gamers).
2. Even merely presenting choices incurs a cost in terms of increasing cognitive load, and I think it's important to avoid inflicting more than is absolutely necessary on newbies. I think it's very likely that analysis paralysis on distro choice is one if the biggest barriers to entry for Linux, and saying "X, Y, and Z are good options" when the person has no clue what the differences between them are or why they should care, instead of just straight-up saying "use X," may be doing them a disservice.