Just NixOS. When building the VM / live CD I copy my dotfiles into the Nix store and then during first boot-up I copy them into my home dir and set up symlinks.
The main reason I decided against home-manager was that it makes my simple symlink setup (~/.foo -> ~/.dotfiles/foo) virtually impossible: Symlinks will always point to the read-only Nix store in one way or another. See https://github.com/nix-community/home-manager/issues/3514 or one of the countless other tickets on the topic. Through this episode I also learned that home-manager isn't exactly well-documented, either, and also quite opinionated. (Which, to be fair, is not a bad thing – if it works for you, it probably works great.)
Finally, not using home-manager was also a risk management decision in that it's probably best to not go all-in on Nix, NixOS, home-manager etc. all at once. Start with the simplest possible config that gets you running, then iterate.
The main reason I decided against home-manager was that it makes my simple symlink setup (~/.foo -> ~/.dotfiles/foo) virtually impossible: Symlinks will always point to the read-only Nix store in one way or another. See https://github.com/nix-community/home-manager/issues/3514 or one of the countless other tickets on the topic. Through this episode I also learned that home-manager isn't exactly well-documented, either, and also quite opinionated. (Which, to be fair, is not a bad thing – if it works for you, it probably works great.)
Finally, not using home-manager was also a risk management decision in that it's probably best to not go all-in on Nix, NixOS, home-manager etc. all at once. Start with the simplest possible config that gets you running, then iterate.