I am ruined by NixOS, so any distribution without declarative configuration and atomic package management with roll-backs, revisions and ad-hoc availability of packages without installing just feels archaic now.

Unfortunately there is no declarative OS that is accessible enough to recommend to casual users (in fact there is only NixOS and Guix and neither has a graphical installer or package manager), and Ubuntu-derivatives offer the least friction so I usually recommend some such flavour.

Below is a bunch of opinions:

I dunno… Ubuntu is in a weird state today. It used to be the distro for new Linux users (well that and Mint), but now that Canonical has given up on the desktop it’s just another apt-based Gnome distro and there are others that do a better job at… whatever it’s trying to do now. Without Unity there’s just nothing special about it any more - it doesn’t have anything going for it besides a still somewhat large user base. There are the flavours for those wanting other DEs but in they’re similarly unremarkable.

The problem with vanilla Ubuntu is that it became so ubiquitous and then suddenly abandoned by Canonical, fracturing the already small Linux desktop community. I think it’s most notably losing the gaming community and Valve is looking for a different distro to support and recommend - that stupid debacle where Canonical announced dropping support for 32-bit libraries with no regard for the consequences I think was the last drop (luckily the decision was reversed after the backlash).

• So it’s not the go-to for gamers. That’s Pop_OS!, Solus or Manjaro.
• It’s not for wow-ing someone into switching to Linux. In fact I don’t even know what distro that would be :(
• It’s not the go-to for moderately technical users; that would probably be Manjaro.
• It’s not for the more principled FOSS activists. That’s more likely to be Guix, Debian, PureOS or one of the more niche ones recommended by FSF.
• It’s not for the enthusiast and developer communities at large; we find our own niche distro. That leaves grandparents, CS courses, offices and “not a computer person” people, I guess.

Regarding derivatives:

Pop_OS! is probably the friction-less Ubuntu-derivative right now. Makes installation and setup very easy. No need to add some PPA for nvidia drivers released in the last few years and they’re even installed by default so there’s no unpleasant surprise for nvidia users trying to game on the terrible Nouveau driver; shitty but ubiquitous proprietary applications are available OotB and some even come pre-installed.

There’s no KDE-focused equivalent to Pop_OS!. KDE Neon should be it, but it isn’t. It for some stupid reason doesn’t provide 32-bit libraries without tinkering in the terminal, so you can’t use Steam OotB even though it’s right there in the software store. When asked about it the response is just “it’s a developer distro!” while the homepage clearly advertises it as an accessible distro with shiny up-to-date KDE software.

Honourable mention goes to ElementaryOS for its doing a good job at filling a niche (rivalling Apple in style), PureOS for carrying the torch in convergence, Linux Mint and Solus for also doing their own thing in a fairly successful manner.

Edit: I should probably commend Canonical and Ubuntu for having helped Linux adoption in the past. Even though it’s no longer what it was, we wouldn’t be here without their efforts.

Edit 2: I forgot to add that I’m quite negatively biased against KDE Neon since I recently converted my friend who after 2 months gave up and went back to Windows. They had been using KDE Neon for around a month or so and an update broke something so they couldn’t log in any more. I would have helped them solve it but it was apparently the final straw.