Right now, it's gotta be Fedora. Hear me out:
- It's stable
- Bugfixes are frequent
- It focuses on FOSS despite being a RedHat distro
- The community is solid
I'd love to know more about Nix though, I keep seeing it pop up in discussions about Linux. Once you get it set up, it seems like a really solid distro that's Arch-like in customizability, but more stable and reproducible. The actually getting set up part though...it scares me.