Go Xen, the market is flooded with OpenVZ providers!
Every man and his dog does OpenVZ, which is pretty easy to use but just doesn't feel the same as using Xen from an adminisrator or vps root user point of view.
It feels real with with Xen, OpenVZ feels a little like knock off goods you can get. (OpenVZ does have it's place! I use it at home for things such as squid to protect the kids - Xen just feels more enterprize )