I run #QubesOS on my desktop and #Proxmox on my servers. If you are only going to have one, I would go with Qubes. Proxmox doesn't come with a GUI and is really meant to be interacted with from another computer. Meanwhile, Qubes makes securely shuffling data around between VMs much easier.

On the flip side, if you can have both, Proxmox has easier comfiguration for getting traffic from the internet into the VM. This can be done in Qubes as well, but they kinda designed the system to prevent the internet from being able to directly get to a VM (other than the sys-net qube).

Hope this helps.