If I wasn’t running Nix then I’m sure I would be running Arch. I like both, generally, but after spending some time with Nix I prefer it for most use cases these days, as I’m a fan of declarative models. There are threads for both Nix and Arch on these forums that will be worth looking through.
Pretty much everything about my nix setup is documented here if you’re interested.
Honestly, either will be good, and you can use nix tooling in arch if you like, to get a hybrid approach and start learning nix.