When comparing NixOS vs openSUSE Tumbleweed, the Slant community recommends NixOS for most people. In the question“What are the best Linux distributions for desktops?” NixOS is ranked 19th while openSUSE Tumbleweed is ranked 60th. The most important reason people chose NixOS is:
Atomic non-destructive upgrades / rollback of a system upgrade / declarative reproducible system configuration / unprivileged installation of packages / transparent source or binary deployment.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro State of the art package manager
Atomic non-destructive upgrades / rollback of a system upgrade / declarative reproducible system configuration / unprivileged installation of packages / transparent source or binary deployment.
Pro Minimal
You can start with a minimal environment and add packages and software to suit your needs as you go along.
Pro Reproducible system
NixOS is configured using the Nix package manager, allowing your system to be replicated and kept in sync across multiple machines. Great for keeping a laptop and desktop in sync.
Pro Robust
Packages don't break after a NixOS upgrade as they are prone to with other distros (especially Arch).
Pro Stable
Tumbleweed is stable enough to use every day. Updates are OpenQA tested to ensure stability before being released for Tumbleweed. Bleeding edge untested software can be tried using OpenSUSE factory.
Pro Easy installation and cutting edge apps
Pro A large amount of software
Pro Tumbleweed + OpenSUSE Build Service
Pro Good selection of preinstalled applications
Pro User friendly + Good support
Active and friendly user community, updates come fast
Cons
Con Documentation is not good
A lot of the documentation of various functions is buried on the source code, their respective manuals, or non-existent. The documentation, the conventions, and the scattered toolchain really made searching for stuff easily missable.
Con A configuration change might end up bricking your system
Con Little / no third-party support
Like it or not, most third parties don't want to deal with less-popular distros. So most of them only support Ubuntu LTS and those versions of RHEL/CentOS that are still supported.