Which caliber for the Prototype Build 7.62x39 or 5.56 Nato

Which caliber for the Prototype Build 7.62x39 or 5.56 Nato?

OK Pandemians, I want to hear from you on which caliber you would like to see a build I have nicknamed the "Prototype" chambered in.  At this point I have a hand selected pre-anodized set of a la naturale receivers from American Spirit Arms, an Ace Ultralight stock, Barnes Precision Machine parts kit, and a 15" Apex Machine free float forend.

Let's hear what you think between 7.62x39 or 5.56 Nato.


UPDATE -
This build has been swapped and changed around considerably since I first embarked on this build.  Origainlly I planned the Apex 15" forend, however I loved that forend on my ASA SIde charger.  Then I attached a Mark IV Geissele forend with a liquidation 5.45x39 Russian surplus ammo chambered barrel seen below. The barrel and handguard were moved to another build and a Carbon FIber AP Industries forend was installed along with a Ballistic Advantage Match Grade 5.45x39 Russian surplus ammo chambered barrel.  Look for the review here http://www.majorpandemic.com/2013/11/A-Tale-of-Two-545x39-AR15-builds-the-Great-the-Good-the-Ugly.html