What is the difference between KVM and OpenVZ?
OpenVZ is a container style of virtualization which relies on the host node's kernel.
KVM has no restrictions in terms of functionality, but it has more overhead than OpenVZ.
OpenVZ is constrained by the host node kernel, but it has less overhead in the containers themselves.
KVM is generally more stable than OpenVZ. However, with that said... do note:
KVM VPSs are not dedicated environments.
Both virtualizations share host CPU and network port among all VPSs.
"...The more you know!"