I'd suggest the .308 and the first reason is, there are no "brush guns" that I know of made in 6.8mm. Other than that the .30 caliber will offer heavier bullet choices for hunting purposes. There are very limited factory loads for the 6.8mm and it's harder to find ammo for anyway. If you are reloading for the 6.8mm you will have more choices, but it doesn't have the power or versatility that the .308 has. You may also consider other popular "brush" choices like the 30-30, .44 mag and .35 rem.