My opinion, for whatever its worth, is that most folks are better off starting with a general purpose rifle like a .30/06 before they get a niche rifle like a .45/70. As a big game rifle, the '06 trumps the .308, but at the risk of repeating myself, the choice of rifle is more important than the cartridge its chambered for. If an example of the rife that really grabs you is only available in a .270, its still the rifle you should buy. But perhaps you prefer a light, short action rifle, in which case a .308 is a good choice, but so is a 7-08 or a .260, if the rifle you want is chambered for the later. If you believe you need a big rifle, a .375 has it all over the .45/70 as an all purpose big game rifle; a .375 H&H or a .375 Ruger, with twice the bullet weight, will shoot as flat as a .30/06, and won't pound you as badly as a hot loaded .45/70 Marlin, provided it fits you.