I used they both in production environments. While VServer uses the 100% of the host operating system resources, OpenVZ resource shortage is very grained: memory, cpu consumption, quotas (two levels, per container and per user/group inside a container), ipfilter entries, etc. OVZ also supports soft and hard limits: You have a memory limit (soft) of 512MB, but also a hard limit of 768MB. Your container may use up to 512 Mb, but if more is needed, it will take up to 768MB.
If you are planning to use all of your machine, Linux-Vserver is your solution due it simple configuration and zero resource checking if any container gets small for their processes, it scales along all your containers.
Now, if you want all control, OpenVZ is the path to follow. But, be careful, you should check if any container is getting small and assign more resources to it. I use OpenVZ for many things, for example, one NS server with 256MB of ram and 5GB disk space.
You should check both and finally choose the one who best fits into your requeriments.