On Ubuntu it’s just an option during installation. So far that’s the easiest install I’ve seen.
OpenSUSE supports a graphical install through their software manager, but I found it caused some issues so I ended up using the command line. That was actually very easy if you’re not uncomfortable using a terminal. Their docs were also accurate and easy to follow.
On fedora I followed the official docs but their instructions didn’t work, so I had to find some thread on a forum with alternate instructions. It took over an hour to get it working.
For sheer ease of use I would definitely stick to Ubuntu since that’s also the only distro Steam officially supports. I’ve had a good experience with OpenSUSE though so I’m sticking with it.