Plus, you have to jump through hoops to install non-free software, which goes against the ethos of Guix anyway.
IMHO, Nix is clearly "the winner" here and we'll see more and more adoption as it improves. Lots of folks are doing exciting work (see https://determinate.systems/, https://devenv.sh/, https://flakehub.com/). And the scale and organization around nixpkgs is damn impressive.
Anyone can create their packages channel or import existing
Also Interesting that you can now install Guix in Nix, or Nix in Guix, or both in any other distro
So you can easily install any package from Nix
There is a lot of work but flakes are still too confusing
So winning is relative
Guix (deliberately) doesn't support anything like the NixOS module semantics. 'Services' are its alternative, of course. I don't know if there is a capability for per-project service declaration in Guix atm, but it wouldn't surprise me!