I'm currently doing my second pass of Nix after diving deep into it last time and coming out unsatisfied. The same problems that I had before with it are problems I'm seeing again:
disjointed configs pulled from random source or build repos on the internet
unintuitive grammars with parameters that require you to download an autocompletion spec
flakes that aren't immediately easy to grok
Contrast that with my last Guix experience:
Lisp form, super easy to understand grammar
Recipes are so trivial that I've written three on my first day
Source tree is included and you are expected to add branches to it
The only problem with Guix that I can see is that it's not as popular
The grammar is really really bad, I prefere a lot the Guix one too! I am using NixOS only because the last time I tried Guix I didn't find a lot of packages for their extremist GNU policy (I agree, but I need some packages), is it still like that?