Comparatively, NixOS is complex, while Arch is simple. NixOS diverges very much from traditional Linux distributions, beginning with using a diferent filesystem hierarchy, which breaks a ton of apps, requiring workarounds like patches, simulating a standard filesystem… In the long run, you will have to deal with many NixOS-specific issues.
Because you’re going to Uni, it’s better to focus on having a mostly just works distro with updated repository, and that’s Arch. On your free time in the future, maybe try NixOS in a VM just so you have a feel for it. And again, you can use Nix on Arch so you use apps from Nixpkgs.
This all comes from an originally Arch user turned into an experienced NixOS user.