Really depends on what kind of disks you have, attitudes towards uptime, performance demands, and flexibility.
Anything ZFS go TrueNAS, but all your disks need to be the same size. This will likely be the most performant setup.
If you want to mix and match disks, you can use Unraid or OpenMediaVault mergerfs + SnapRAID. Note they are not equivalent, and there are performance implications.
Or classic Linux install with standard CLI tools for creating an array, setting up VMs, etc.
I would spend some time with each of the above three popular NAS OS, especially if you are going to be the one managing it.