Is KVM better than OpenVZ?

Definitely not!! (But I may be biased) The difference between KVM and OpenVZ stems from the fact the two solutions offer two distinct types of virtualization. KVM’s hardware-level virtualization requires a hypervisor, which, in this case, is the server itself. You need computing power to run the hypervisor, which means you can’t distribute all system resources among the guest machines. Some of them need to be reserved for the hypervisor. The OS-level virtualization offered by OpenVZ deals away with the need for a fully-fledged hypervisor, and you can run all its containers with very little overhead on the host’s resources. It’s estimated that as much as 99% of the physical server’s hardware can be safely distributed among containers. https://openvz.org/