I'm a Guix core developer, so my answers below will of course be biased towards Guix. >what are the relative merits of Guile and the Nix expression language, i

I'm a Guix core developer, so my answers below will of course be biased towards Guix. >what are the relative merits of Guile and the Nix expression language, in practice? Nix is a DSL, whereas Guile is a general-purpose programming language. In practice, I find it better to use a general-purpose language, because you have access to all of the features of that language and its libraries for free. >How big is each community? I don't have any stats, but the Nix community is definitely bigger. Both communities are very active. The guix-devel mailing list and the #guix IRC channel are busy places. https://lists.gnu.org/archive/html/guix-devel/2015-02/threads.html https://lists.gnu.org/archive/html/guix-devel/2015-02/thread... >The Guix package list is much smaller than the NixOS list? Yes. The Guix package list is rapidly growing, though. Patches for new packages come in every day. Our last release had 164 new packages. Hope this helps!