.308 is considered the more accurate cartridge, but I think you won't notice the difference until you get into benchrest target guns. In a H&R, the ultra comp barrels seem pretty accurate, but they are out of 30-06, although they might still have a few 270win.
I just got a barrel order from H&R, I ended up going with the .308 because I could get it in a bull barrel. I might end up making a 30-06AI out of it. (or maybe even a 30-280AI, as I already have a 280 ackley improved reamer)