For some context, I believe many/most people doing PAAS (e.g. Heroku, DotCloud, Cloudbees, Node*) are using LXC to create slices/dynos/shards/whatever.
In the 2nd half of 2011 other PaaS players caught on to the wonders of container virtualization - Heroku for example started using it with their Cedar stack in April of last year.
I am considering to use one of those for securing / hardening a set of VPSs I am using. Since I do not have debt with any of these tools, I would like to start with just one. The question is which one?
I would only use OpenVZ if there is a particular feature that it does better, and you can't afford to wait for LXC to catch up.