Void for desktop/laptop. These are the things I like about it.
- Rolling release
- Initial installation is minimal, and doesn’t foist a specific DE or other unessential software on me.
- No systemd
- Nothing similar to Arch’s AUR. I know a lot of people love it, but I do not. I mention as the distros are similar.
Debian for my server. But I plan to migrate to Devuan.
- Stable and well tested
- Huge package selection
- Pretty ubiquitously supported. If for whatever reason what you want to run isn’t in the repo, .deb packages and apt repos are often available.
- Minimal installation available.
NixOS is a declarative distro. Meaning it you can declare pretty much every aspect of it from what software is installed to how the system is configured from a config file.
Using you calandar example, you can list Thunderbird (or whatever) as a package you want in the configuration and it will be installed. You can also use that same configuration on another machine and produce the same environment.
Relevant to the original point, since all your software is listed in a text file, you can easily see exactly what’s installed.