A KVM (do not confuse with KVM rescue for server fix) VPS is like a dedicated server within a physical dedicated server. OpenVZ shares resources with every other client on the host node and is considered container based virtualization. You should choose what is right for you based upon your needs. If you need help deciding, ask someone from our sales team and we'd be glad to point you in the right direction.
* KVM for VPS is completely different from KVM rescue mode (console).