They all have their pros and cons to be honest but i believe that solusvm is one of the best if not the best. Unless you want to create a custom panel which would be ideal if you can afford it or if you can make it on your own. but my vote goes to solusvm hands down as i have tried and tested many of these in the past to figure out what the best solution for us would be.
I would suggest you to have SoulsVM control panel to manage your VPS, Solus Virtual Manager (SolusVM) is a powerful GUI based VPS management system with full OpenVZ, Linux KVM, Xen Paravirtualization and Xen HVM support. SolusVM allows you and your clients to manage a VPS cluster with security & ease.