Given the direction that the Nix project is going, I suspect that many of you Nix users reading along here are currently considering alternatives, and among them Guix.
Personally I've only been using Nix for a few weeks, so my investment is not that big, but how about you? For a technical comparison, you could start with these two articles. If you're on IRC, I'd also suggest to join #guix just in case or look at the other communication options they endorse on their website.
What gives me the most thoughts is the availability of recent-ish software on Guix; but given Guix's FSF-level copyleft culture there's at least the certainty that whatever efforts I might put in to build and package things myself would have the lowest-possible likelihood of suffering corporate/fashtech capture. And we may be picking up momentum to collectively alleviate those problems.
I'll definitely try to move the people I know who are interested in/users of NixOS over to Guix. Admittedly, there aren't many to begin with haha.