Wow. Check out this article:
Lab Experiment: Hypervisors
http://virtualizationreview.com/features/article.aspx?editorialsid=2641
There was no overall winner here; no way to say, "This is the best hypervisor for every situation." But some general conclusions can be drawn. For CPU- and memory-intensive applications, XenServer and Hyper-V are attractive and have proven their mettle. For a large number of light to moderate workloads-or if you decide that memory over commit, for example, is important-ESX may be the answer. What is entirely clear, however, is that all three hypervisors are legitimate virtualization platforms, and that no single company has a monopoly on virtualization any longer.
So if I read this correctly, the most expensive hypervisor appears to also be the slowest in most cases.
Hyper-V won 4 of the 11 tests (the others going to XenServer by a less than a horse length). For example, test 2 focused on a large number of heavy workload systems: 1 database server running one midsize database and 12 VMs with a heavy workload of CPU, memory and disk operations. In the test, Hyper-V completed SQLjob 52% faster than ESX, was 2.3 times faster than VMware ESX in CPU for Virtualization Review’s hypervisor test operations, and was 3 times faster than VMware ESX in test for average RAM operations.
Note: I’ve recently heard a rumor that there’s a possibility a certain vendor may attempt to get this article pulled from the web site so if you want to read it, I suggest you take a look at it ASAP.
Kurt Shintaku's Blog 