We are running SolusVM and we are currently testing ProxMox for some features we are after.
Proxmox is an excellent solution quite versatile packed with a lot of features. KVM runs very well and deliver excellent performances.
I have used proxmox for a few years now and its been really stable. No issues yet.
We have tested the cluster features within proxmox which is a really cool feature.
But I would choose proxmox for more advanced users and virtualizor for less advanced users.