Remember the days when everyone and their pet iguana was raving about Arch Linux? You couldn't escape the ever-so-subtle "I use Arch BTW" remarks in every Linux forum. Well, move over, Arch, because NixOS is here to steal your thunder! Nowadays, it seems that you can't browse YouTube or read a blog ...
Fun fact: I use NixOS since six years now and at least in the first two years the Arch Wiki helped me a lot to understand the NixOS configuration options.
That's the main crux with NixOS, it does a lot of stuff in the background for you that in my opinion you should know why it's being done the way it is. As such I consider Arch a good distro for a beginner who wants to learn the inner workings of Linux, while NixOS is a better-engineered distribution that takes care of the system for you. Arch's goal is to be simple for the maintainers which means it's very close to what one might consider a "standard Linux", and its wiki is mostly a documentation of exactly that.