Current best practice for Time service settings for Hyper-V 2012 R2 Host and guest OS's

I am trying to find out what the current best practice is for Time service settings in a Hyper-V 2012 environment. I find conflicting information. Can anyone point me in the right direction. I have found some different sources (links below) but again the are not consistent. Thanks

http://blogs.msdn.com/b/virtual_pc_guy/archive/2010/11/19/time-synchronization-in-hyper-v.aspx

http://technet.microsoft.com/en-us/library/virtual_active_directory_domain_controller_virtualization_hyperv(v=ws.10).aspx

http://social.technet.microsoft.com/wiki/contents/articles/12709.time-services-for-a-domain-controller-on-hyper-v.aspx