What distro do you use and why?

All that follows is my personal opinion, but for ease of writing, I'm gonna present it as facts.

Once you have grasped the advantage that Nix offers, all the fundamentally different solutions just seem s o inferior. When I first tried NixOS on a decommissioned notebook, the concept immediately made sense. Granted, I didn't understand the language features very well – I mostly used it for static configuration with most stuff just written verbatim in configuration.nix, though I did use flakes very early on because of Lanzaboote. But just the fact that you had a central configuration in a single language that was able to cross-reference itself across different parts of the system absolutely blew me out of the water. I was a very happy and content Arch user, even proficient enough to run my own online repository that built from a clean chroot for AUR packages (if you use Arch with AUR packages on multiple systems, check out the awesome aurutils!), but after seeing the power of NixOS in action, I switched over all my machines as soon as I could - desktop, virtual servers (thanks nixos-anywhere!), main notebook and NAS.

People often praise the BSDs for their integrated approach – NixOS manages to bring that approach to Linux. Apart from GUIX System that I never tried because Secure Boot was a requirement when I last looked at other distributions, none of them have tackled the problem that NixOS solves, and it's not even certain if they actually understand it. Conceptually, it plays on a whole different level. No more unrecoverable systems, even with broken kernels – just boot the previous configuration. Want to try changes without any commitment? nixos-rebuild test got you. Need an app quick? nix shell nixpkgs#app it is.

Plus the ecosystem is just fantastic. The aforementioned nixos-anywhere really helps with remote provisioning, using disko to declaratively setup filesystems and mounts, you have devenv which is a really good solution for development environments, both regarding reproducibility and features, and many more that I can't mention here. There is nothing comparable, and the possibilities are unlike in any other ecosystem.

It's not perfect for sure though, and documentation is sparse. The language concepts which allow one to "unlock" the most powerful features are different from what most people know.

I was lucky enough to have some downtime at work to get into the system a bit deeper (this was still for work though, just not my core skillset) by implementing a "framework" for our needs which forced me to not just copy and paste stuff, though I definitely did get inspired from other solutions, but to actually better understand the module system (I think?), thinking in attribute sets, writing your own actual modules, function library and so on. But in the end, it was definitely worth it, and I'm unaware of any other system that would allow what Nix and NixOS allowed me to build.

this but since Nix is licensed with MIT and deals with weapon manufacturers, i had to go

GUIX!!!, it is everything