As a webmaster, I definitely prefer XEN over anything for the dedicated resources that I am assured of.
People generally tend to think that if a Webhost is selling OpenVZ VPS, they are going to be oversold. Which I can tell you, is not that easy a case as it seems. At least not in our case. We have a node for OpenVZ VPS which has about 16GB DDR3 RAM on it. So if it were to be dedicated to resources(like in case of XEN), it could fit in at most 31 VPS of 512MB RAM each.
But then we all know that all 31 VPS aren't going to run in full operation simultaneously at all times. This is where OpenVZ does provide greater flexibility. You could easily fit in another 10-15 VPS and still make sure that your node isn't going to blow up.