I operate a linux server offering shared hosting plans but I know that alot of higher end clients demand root access and system control via either dedicated or vps solutions. I'm looking to starting vps servers because im currently not able to offer dedicated servers.

I'v been doing research but there are a lot of open source vps solutions out there so I'm looking for opinions on which is the best, and easiest to setup and maintain.

Here are my choices
openvz
linux-vserver
vmware free edition

They will be running on RHEL AS 4 and centOS 4.4 machines

Are there any vps systems Im missing. Which one should I go with?