I like that the NixOS packaging system feels like it’s build for Free Software, making source code and Git repositories a first class citizen. You can simply drop a flake.nix into your repository and turn it into a Nix package within a couple of minutes, that’s quite a bit different than the utter headache it is to package something for Debian. Nix packages being free of naming conflicts also makes it very easy to mix and match whatever versions you need, something that’s basically impossible on most other distros unless you resort to containers or virtual machines. NixOS having the largest package collection of any distro is a plus too.