<p class="line862">It looks like ESXi is the way to go-- it's free (until you want to upgrade it to the vSphere feature set), and apparently has a better architecture. It also looks like it's going to be the main focus hypervisor-wise for VMware moving forward. This was posted on the ESXi team blog on the VMware site:</p>
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<p class="line862">VMware made the decision to make <a class="http" href="http://vmware.com/download/esxi/">VMware ESXi, our next generation hypervisor, freely available</a> to proliferate the VMware platform and allow administrators to prove its value at no cost. However, the fact that the older platform, VMware ESX, is not also available for free has lead some people to believe that ESXi may be inferior or not as feature-rich as ESX. This is certainly not the case. In fact, the opposite is true.</p>
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<p class="line862">ESXi has a superior architecture and we encourage customers to deploy ESXi as part of any new vSphere deployment. Our future posts will compare ESX 4 and ESXi 4 in detail on topics like hardware compatibility list, performance, and management to demonstrate that ESXi is either on par with or superior than ESX. But for now, here are some key points you should know about ESXi vs. ESX:</p>

<ol type="1">
	<li>The functionality and performance of VMware ESX and ESXi are the same; the difference between the two hypervisors resides in their packaging architecture and operational management. VMware ESXi is the latest hypervisor architecture from VMware. It has an ultra thin footprint with no reliance on a general-purpose OS, setting a new bar for security and reliability (learn more).</li>
	<li>In the future, ESXi’s superior architecture will be the exclusive focus of VMware's development efforts.</li>
	<li>New and existing customers are highly encouraged to deploy ESXi. Many Fortune 100 companies have already standardized on the ESXi platform.</li>
</ol>