SteamOS has a UI best for couch-gaming. For desktop a regular DE should be better.
Mint and Ubuntu are easy to configure and beginner friendly. And most companies only list support for the Ubuntu LTS.
I'm using a mix of Xubuntu on my Laptop and Xubuntu with KDE on my Desktop. And Debian on my server.
I think I will go with debian on the next install, because now I am capable enough to install the graphics-drivers without the Ubuntu-Software-Centre.
But any Distro should be fine.
If you like to fickle a lot Arch, or gentoo might be worth checking out.
For the Desktop environment XFCE ist light, configurable and fast. I had an annoying bug on XFCE I could not solve, therefore I use KDE now.
