Calling NixOS an "academical experiment" is slightly disingenuous. The initial author does come from academia, but works in industry now, and you just need to look at the Github [1] to see that NixOS is maintained quite actively.
I concur. Besides NixOS is certainly more polished right now, at least for my definition of "polish" (I think, the right word for Scheme based Guix is "cohesive", maybe even "elegant"). It should be, being several years old, compared to Guix, which has been running on real hardware for mere weeks.
[1] https://github.com/NixOS/nixpkgs/commits/master