One caution though -- being a GNU project, Guix takes a much stronger stance on non-free software than Nix does. In Nix, there's a flag you can enable that will let you build non-free software in the Nixpkgs repository. I don't believe the same flag exists in Guix.

Note that either system could be used to build your own non-free software, this is more a question of what is available in the shared repositories.