Windows Server 2008 R2 or Windows Server 2012? Which one is your personal choice?

Windows2012, Because it allows you to centralize and consolidate both monitoring and control of various windows environment that you have deployed.

actually i'm using the two, it depend on your need, like2012 is  centralized and better for clustering and big data (cloud), and more powerful than2008

My Preference for Windows2008 R2 enterprise Edition 64-bit and i was using it around4-5 year and there are not such bugs and working good for and i also using Active Directory, DNS, DHCP, IIS, File Server and SQL Server2008 R2 Enterprise edition64-bit services they all working Good and i never face any such issue.

Win2012 R2 so we get get all new features, especially the virtualization with public and private cloud solutions, in a addition you can avoid a lot of comparability issues which is related to virtualization (like hosting Linux VM)

that would depend on what you hardware is and what task you want to carry

2012 R2 Std

For your question my answer is Windows Server2008 R2 but there is better then both you ask and it's Windows Server2012 R2 it's better than Windows Server2012 and2008 R2