I have a VPS with WiredTree and am very satisfied; however, I am not a huge fan of Virtuozzo/OpenVZ. I greatly prefer Xen as you are able to have swap memory. When you run out of RAM with Virtuozzo/OpenVZ, it starts killing off processes, which for me is not preferable since my VPS only spikes very occasionally and can be frustrating when services are temporarily unavailable even for short periods.
For Xen VPSes I highly recommend Linode. It is completely unmanaged so you will need to know how to administer a Linux server. They have a lot of awesome advanced network features such as IP fail over and out of band console access which is great if you screw something up. Their support answers within 15 minutes but you have to remember it is 100% unmanaged. If you need handholding, WiredTree would be a better option since its managed.