Another recommendation for Linux Mint here. I've bounced between Manjaro, Ubuntu, Fedora, and I've found Linux Mint to just be fantastic for beginners, in that everything just works, and it does a great job of guiding the user through installation, updating drivers, updating packages (including choosing an appropriate package mirror), and setting up backups.
It's just really nice all around; the only thing I could complain about is lack of touchpad gesture support, but that's probably not an issue for desktop PC usage.
Happy paying customer here, it's great to see the innovations they're making and their interactions with the community.