Linux

I've been using it for around a year and really like it so far. It is however very different from almost every other linux distro, so I would think carefully about it before switching. If you're not prepared to invest significant time and/or don't really care about the advantages of NixOS, you should stay away from it.

Pros of NixOS:

• Declarative configuration: This is probably the main selling point. The whole system configuration and installed packages are neatly in one place. Using home-manager, this can also replace config files for many programs. All of this is especially useful if you share that configuration between multiple devices.
• System rollbacks: If something breaks, simply boot into the previous generation.
• Very customizable system: You can freely choose your desktop environment & basic system packages.

Pros of Nix in general (you don't need to install NixOS for this):

• Huge package repository (also very up-to-date if you want to use the unstable channel)
• Consistent developer environments that can easily be shared

Cons of Nix & NixOS:

• Very steep learning curve: You essentially have to learn (the basics of) the Nix programming language.
• There are often many ways to do things without any clear recommendation: Channels / Flakes, whether nix-env should be used, etc.
• The documentation isn't always great (although it is improving)
• If something is not packaged in nixpkgs, it can be difficult to run it, since NixOS doesn't follow the Filesystem Hierarchy Standard. There are some tools to run flatpaks, appimages and arbitrary executables, but especially the later might not always work out of the box.