Ubuntu would be the smartest choice. It's got the best support of any Linux distro, and you can install Steam on it just fine with the deb.
Not that I'm saying that Debian is a better choice than Ubuntu here – Debian stable is Debian stable, and Ubuntu often contains stuff still considered experimental on Debian side – but unlike with, say, Fedora, many non-free drivers are included in the official repositories.
The reason I mention Ubuntu is that the community is just much larger than that of Debian and there is more of a chance of someone already having solved any issues you may run into.
Ubuntu is the distro everyone is targeting so for seamless experience you kinda need to stick with it.
(That doesn't mean other distros won't work tho.)
Ubuntu is the only officially supported distro, as in mentioned in system requirements, just because it's the most ubiquitous distro. It doesn't actually mean you will have any less problems with the problematic Linux games on Ubuntu, than on any other distro.
On Arch, with an NVIDIA card, getting this "all" up and running boils down to: sudo pacman -S steam nvidia
This gives you the most recent NVIDIA driver, 378.13-5.