I use both Proxmox and libvirt on Debian. I don't use clustering. For me, the biggest advantages of PVE are:
Good VNC and serial console support integrated into the web interface. (Could probably get something similar with libvirt using Guacamole, but PVE makes it super easy).
Good VM snapshot management. I've found libvirt snapshot management to be pretty limited and/or buggy, and I've had to resort to directly operating on qcow2 files.
On the other hand, there are a couple things I like more about libvirt:
Good support for SR-IOV NICs. libvirt lets you create a pool of VFs and automatically assign a free VF to a VM. (It's a little surprising to me that PVE doesn't do better in this area.)
Simpler with fewer moving parts to break.
I use libvirt for my most critical VMs (network infra like router, DNS, and DHCP). I strongly prefer PVE for anything where I'm going to be interacting with VMs regularly, like testing or lab setups.
I use both Proxmox and libvirt on Debian. I don't use clustering. For me, the biggest advantages of PVE are:
On the other hand, there are a couple things I like more about libvirt:
I use libvirt for my most critical VMs (network infra like router, DNS, and DHCP). I strongly prefer PVE for anything where I'm going to be interacting with VMs regularly, like testing or lab setups.