Hi folks, author here. Happy to answer questions.
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Myself and my family are running Fedora's KDE edition. The Fedora team has a long history of working very closely with the Plasma dev team, quite actively contributes upstream, and I haven't been disappointed. I'd vouch for this one from first-hand experience!
We also have a new project to produce a distro of our own in the works, called KDE Linux. That has recently had its first alpha release. It still has some real feature gaps and may not serve you well if one of the missing bits is something you require, but it's definitely worth looking into. It has a lot of next-gen ideas baked and some things we got to learn during the SteamOS effort, and think it has a place in the ecosystem.
In the dev community I generally see a lot of people running KDE on Arch, Debian and openSUSE as well.
The company stuff in the background doesn't really matter.
The team working on KDE Linux are motivated by addressing some structural challenges that always plagued KDE Neon from the concept of trying to graft more recent SW on top of the Ubuntu LTS base, plus some lessons learned from the SteamOS project's way of handling updates, and fully utilizing more recent Linux/systemd features.
It's sufficiently different that sticking with the Neon brand and swapping it out for that userbase would have been pretty disruptive, so they felt it was better to go with a distinct identity.