So Elementary OS is essentially what Redhat Linux used to advertise itself as, but never quite was? A comprehensive, integrated desktop OS built on GNU/Linux?
This is true so long as they're not in some need to always be using the latest kernel or packages (e.g. casually curious desktop user, or developers looking to use standard interblag languages/tools). People who are setting up the machine for their parents or aunt or uncle, or who are just wanting to "get into Linux" by using it some of the time.
Both of them focus on an approachable UX, OOTB functionality, and stability. Updates tend to be minor desktop-centric improvements, building on the same kernel and base packages over a year-and-some period, as they are both built on top of Ubuntu LTS. Things change less often, so they break less often.
If they really do desire some newer software version that isn't backed by the Ubuntu LTS, the PPA system is there to fall back on. It's certainly no AUR, but for people who want a very middle-of-the-road experience, where the OS gets out of your way so you can get things done, it's a decent balance.
I have not experienced the version upgrade experience in Elementary for a while, but in Mint I have had better experiences with version upgrades than with any other non-rolling desktop distro. Reliable version upgrades are an under-appreciated aspect by longtime Linux nerds (myself included) who think nothing of a quick backup and re-install because of segmented /home partitions, have self-hosted backup systems, or other such advanced configurations. It is the main reason I don't recommend the non-LTS Ubuntu desktops, because of the number of times I have seen the upgrade go awry for less savvy users, e.g. from 17.04 to 17.10.
As a final note, the only reason I don't recommend Pop! or Ubuntu itself, is how unfamiliar the GNOME interface metaphors tend to feel to newbies. I realize other people completely disagree with this approach when recommending Linux distros.
Pop's desktop environment looks like a barely customized Gnome3 session to me. I'm not sure I would even call it a fork. Looks more like just a theme.
Pantheon (Elementary) is more of a fork of Gnome3, reusing some low level parts but presenting a much different experience to the user.
They have collaborated with elementary in a few areas though. Instead of gnome software, they have Pop Shop, which I believe is a fork of the elementary app center.
They also use their own installer, which I believe was a collaboration with elementary os.
While I have sympathies for System76 and Debian, there is no way I am going to install an OS with this name.
- How am I supposed to pronounce this? pop? popos? pop-OS? What should I do with the special characters?
- What happens if I accidentally paste this into the shell?
- What associations should the name "Pop!_OS" have? Appart from the english "pop open" something, in German there is: "Popo" -> Childs word for "bum", "poppen" -> "to hump". Both not exactly favorable.
Also, who comes up with names like this? Have you talked to any marketing person to this before deciding on a name. If you want professionals to put this on their machines, better make sure it sounds vaguely like something you might be able to put trust into.