Scheme is a more mature and more expressive language than Nix imo. And you can write your home configs in scheme too.
The differences aren’t that big, nix is great but I find (at least I did two years ago) the documentation a bit confusing. Both are great. I like scheme a lot better than Nix (the language), and the tooling is a bit less confusing to me.
I didn’t know about home-manager, but it seems like it.