I've been using Virtualizor for a few days now and I am beyond happy! I tried SolusVM, Proxmox, Parallels and HyperVM before trying Virtualizor and I must say nothing compares.
Support for XenServer and all virtualization types, a large database of OS images, flawless networking support (bandwidth limitation and tracking!), simple billing model, helpful and fast support and the amazing WHMCS module, great documentation, I could go on for days.