The 6.8 is a solid round. The ammor is available but expensive.
If you want long range/flat shooting and aren't necessarily tied to a larger bullet, the .204 Ruger is phenominal, though the power on man-sized targets is lacking.
If you want cheap ammo and a .30 cal type platform, there is always the 7.62x39. I haven't found the reliability problems with it that some have.
All around though, I think the best all around option of long range, decent power, and ammo availability is the 5.56. If only we could get an AR upper in 5.45 x 39, which is an impressive little round.
If you want long range/flat shooting and aren't necessarily tied to a larger bullet, the .204 Ruger is phenominal, though the power on man-sized targets is lacking.
If you want cheap ammo and a .30 cal type platform, there is always the 7.62x39. I haven't found the reliability problems with it that some have.
All around though, I think the best all around option of long range, decent power, and ammo availability is the 5.56. If only we could get an AR upper in 5.45 x 39, which is an impressive little round.