I have zero experience with pkgsrc. From a first glance (from pkgsrc.org), I can say that nix claims to have 80k packages whereas pkgsrc 26k. Also, nix'es main selling point is reproducible builds, which is pretty cool. Other than that, nix is satisfactorily fast (much faster than homebrew, not sure in comparison to pkgsrc).

I landed on macports after trying to follow the instructions for pkgsrc and the signatures/PGP keys were out of sync...

Now I've moved partially to homebrew due to better community support - and lack of arm builds for macports.

https://build.macports.org/buildslaves