I have both calibers..the 7-30 is a 16" carbine barrel and the 6.8 is the new G2 23" rifle barrel.  I like them both, but between my two barrels and my handloads, I believe the 6.8 is more accurate..alot of factors involved..one's a short tapered barrel and the others a 23" almost bull barrel.  There are far more factory loads available for the 6.8 than the 7-30.  The 7-30 will handle heavier bullets than the 6.8 if that is a factor.  7-30's can be made from 30-30s brass (usually free firing range brass).  6.8 is expensive at the moment as is most other brass.  I believe the 6.8 to be the ultimate beginners rifle..hardly any recoil.