[maroon93]

KVM has much better isolation than OpenVZ and in my experience KVM gets better performance as well. However I've heard some say they get better performance from OpenVZ. KVM has come a long way in the past year though, so I wouldn't be surprised if it's surpassed OpenVZ by now... :idea:
KVM also supports any operating system (in theory), whereas OpenVZ is limited to Linux only.
We're using KVM exclusively for our virtualization systems and have no interest in switching to anything else.