On his blog, Keith Mayer wrote a very good comparison between Windows Server 2012 R2 with System Center R2 and VMware vSphere 5.5 Enterprise Plus + vCenter Server 5.5.
I would highly suggest you to read this article, it’s a good and well researched comparison.
Read more here.
With day 1 and right to the keynote from Ben Armstrong, the preview of Windows Server 2012 R2 and System Center 2012 R2 is available.
You can find them in the TechNet Evaluation Center: