I've only been running NixOS (in any serious capacity) for three years, but I have installed it on every computer that I am allowed to install it on now.

It has been the most headache-free Linux I've used, simply because I'm less scared to play with and fix stuff. The fact that rollbacks are trivial and snapshots are automatic, and since everything is declarative in a text file anyway, I am way braver. If I do something like screw up the video driver, or the wifi driver or make it so the system doesn't boot anymore, all I need to do is reboot and choose a previous generation.