I understand you're planning to build a private cloud based on OVM.
In general terms we can safely say that the latest version is always the best choice. Oracle generally fixes all high impacting known bugs before a new release, plus introduces a number of enhancements that add value to the newer product. There is no reason to believe that an older version would be more stable, unless a specific unknown bug exists in the newer version.
You can find more information on Oracle VM at http://www.oracle.com/us/technologies/virtualization/oraclevm/overview/index.html .
You may also want to explore the Private Cloud page at http://www.oracle.com/us/solutions/cloud/private/overview/index.html .
Oracle OVM 3.2 providing greater operational efficiency with improved ease-of-use, and more automated processes including full command-line support.
Designed for ease of use and rapid deployment, new features of Oracle VM 3.2 include: