My choice would depend on the intended use.
6.8 SPC factory ammo isn't cheap, if you handload I spose it's no different than anything else.
Saw an episode of Guns and Ammo TV where Richard Venola showed off his tricked-out 30 in 6.8, he uses it for P Dogs at 300 yards- and it sits by his front door for SD. For hunting, or where accuracy counts, I'd go with the better ballistics of the 6.8
For plinking, and spray and pray with cheap ammo, you can't beat the 7.62 x 39 as said above.