If you haven't already checked out this article from Greg Shields, I invite you to do so.  This is a really good article that takes a look at the architectural differences between Microsoft's Hyper-V and VMware's ESX platforms.

In this Realtime Community blog post, Shields is trying to take a balanced view on the differences in the architectures.  When talking about raw performance, he writes:

Here's another extremely important point, and one which is a primary reason why Hyper-V will generally always beat ESX in terms of raw performance: Hyper-V is a "Microkernalized Type 1" hypervisor which leverages paravirtualization. ESX is different in that it is a "Monolithic Type 1" hypervisor which leverages hardware emulation. This is a key difference and it's where the functional differences exist between the two approaches. Let me explain:

Hyper-V is considered "microkernalized" because its drivers are all installed into its administrative OS and not into the hypervisor itself. For that reason, Hyper-V's hypervisor is only around 260K in size as compared to ESX's 32M. I usually joke with people at this point that, "with a hypervisor of this size, we're talking about Atari 2600-type coding here." It is extremely small, extremely optimized. The smaller the hypervisor, the faster it can be due to code optimizations, the more secure it can be due to fewer interface endpoints and sheer code itself, which equals what amounts to a more bombproof solution.

However, anytime someone says anything about comparing Microsoft and VMware, the factions come out to protest something that is stated within the article by submitting their own comments on the matter.  And this article is no exception.  Like their operating system, there are plenty of people who don't want you messing with or talking bad about their hypervisor!!! 

I've read numerous articles from Greg Shields on Redmond Magazine over the years, and like many of his other articles, this one is also worth the read.  Whether you agree with his findings or not... well, I suppose that will determine if you leave him a comment or not, now doesn't it?  ;)