Could not find any documentation on which server would be "better". Production AD is on 2008.
take a Look at the Support.mcafee.com. There you can find the supported Environments for any McAfee product.
McAfee Corporate KB - Supported platforms, environments, and operating systems for ePolicy Orchestra...
Since Win2008R2 EOL was 1/13/15 (unless purchased 6 year extended plan) I would really consider installing ePO on Win2012.