Regarding the biggest: nixpkgs sits at around 140k packages, way more than others.
Best: I still argue that Docker and Conda are more accessible, but my point was to go for reproducible, declarative science. Nix environments are exactly that. They're not perfect and are, as you point out, not standardized. But they cover much more ground that Docker. If you trust the upstream nix repo, you can get bit-level equality at every single build you (or anyone else) does. Docker relies on huge binary blobs that you can't inspect and that can be pretty much arbitrarily swapped around.
I'm totally fine if Guix takes over. Or the next big thing. As long as it's declarative and reproducible.
Best: I still argue that Docker and Conda are more accessible, but my point was to go for reproducible, declarative science. Nix environments are exactly that. They're not perfect and are, as you point out, not standardized. But they cover much more ground that Docker. If you trust the upstream nix repo, you can get bit-level equality at every single build you (or anyone else) does. Docker relies on huge binary blobs that you can't inspect and that can be pretty much arbitrarily swapped around.
I'm totally fine if Guix takes over. Or the next big thing. As long as it's declarative and reproducible.