If you are doing a fresh install, you might as well use Debian. It’s a little lighter weight as an OS than Ubuntu, but it’s not really going to make a massive difference at the end of the day - you’ll be running unsupported anyway.
You could also look at using Proxmox and running HA OS in a VM, and then run another VM with Ubuntu/Other Distro for anything else you want to install, gives you the best of both worlds and is considered fully supported. This is how I run things now and it works very well.