I have both nix and guix stores on my (voidlinux) system just trying them out. Package availability seems quite different between the two, and guix feels like it's heavier or slower, but I am biased to guix's shepard instead of systemd.
Initially, I really wanted to use Guix over Nix, but Nix is more mature with more packages, maintainers, and features.
Last I checked, for example, there was no equivalent of a channel or overlay in Guix. Their npm importer was also not released, whereas Nix has a very usable node2nix.
Having done virtually no functional programming, learning Guile Scheme was also a barrier to me, but the Nix expression language felt a lot more natural for whatever reason.
It's unfortunate - I'm very interested in the work in reproducible builds and substitutions Guix has done, maybe it'll take off at some point or those features will be integrated into NixOS.
As an end user you don't really need to know Scheme. The OS configuration and package definitions are very "DSL-like", but you do have the full power of Scheme available.
[0] https://www.gnu.org/software/guix/manual/guix.html#Package-M...