some comments.

• both are absolutely fine for a university laptop, though very different.
• NixOS is more stable. It is almost impossible to brick it, you would have to delete every working old generation.
• nixpkgs is like arch repos plus AUR together. nixpkgs is actually one of the biggest repos if not the biggest repo at the moment. so no problems there.
• i mean, this is like highly subjective and my own opinion: go with NixOS, it's just a cooler OS imo and your system and your abilities will only get better with time. and it's fully reproducible by design, so almost every bit of work you put into it will be worth it, in some sense. i also believe that NixOS will become much much more relevant in the future. bigger community, better documentation, more resources!
• ...unless you don't want to put a lot of time in it in the beginning. it will most likely be really frustrating and it will distract you from other dtuff you want to do on your computer. like just getting browser email editor etc. you will have a setup no problem pretty quickly. it won't be more than just puttung the programs you need in your systempackages. but then you realize you need vpn, or a dropbox client, or some audio setup, and other stuff, and before you know it you are spending hours and hours or weeks trying to find out how this works... this is, i would say, the major "downside" of NixOS conpared to arch
• if you can afford trying it out and then switching to something else and starting over again, try out NixOS!