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 first installed guix (using this guide) onto an old desktop I had to get a feel for it. Then, when a system update on my laptop (manjaro) went sideways I installed guix onto that and never looked back.
It does have some caveats. Some packages don't exist in the official repo, but thankfully you can have as many channels as you want and get packages from other repos (nonguix being the biggest). Ironically for applications for with a guix package doesn't exist, I use nix.
Some DEs aren't available (KDE forex).
Despite the above issues I really like guix. I like the transactable nature of system and package upgrades (same/similiar functionality as nix). J
Just like nix your system config is declaritive (in scheme a file/files) and you can rollback configs. I'm more likely to try things/update my config because I can just rollback if something goes wrong.