Those two are very different imo. Proxmox as a hypervisor would give you the most flexibility, but the question is whether you'd actually need that flexibility. You would also need to decide further how you implement your setup within it.

unRAID would have the advantage of a large community and lots of guides. Downside is that it costs money, which could also be used towards better hardware.

Personally I am reasonably happy with openmediavault and have my media server setup with that (jellyfish+and arr apps with docker compose). That could also be an option.

Another alternative might be something like CasaOS, which would give you a probably simple to use app store that maybe covers your needs already.