Unfortunately, the 45-70 is one of those calibers that only one gun in the caliber would never do. I've got my first 45-70 gun, a Marlin 1895, with a 22 inch barrel. Its got a few scars, and been used a lot with pigs, bison and elk with a couple of deer and what I used when I experimented with loads. It shot a bit of jacketed bullets before I got into cast. 45-70's are one of the best cast platforms. Whether you cast or not it doesn't matter, the 45-70 should be reloaded. Very effective loads exist in the lowest pressure (trapdoor) that take very large game with ease. Higher pressure simply is not needed. Most of us have to check them out. I was one that loaded on the higher end and discovered that a big chunk of flying lead is going to kill and usually have an exit no matter the bullet or speed. I also have the 1895GS, and a 1895CB. All are fun, and what I use when I need repeaters. For the most part, hunting can easily be done with a single shot. I've got a Buffalo Classic and a Ruger #1 as well. The Ruger is short, handy, and very accurate. It can shoot the higher pressure loads, but is not particularly fun to use with them. I also have a Baikal double barrel I got primarily for fun. Its accurate with my reloads, and probably what I'll use here in the Fall after bow season.
A 45-70 is probably not necessary for most folks. I've used it like I have to increase the challenge and pleasure of hunting. Kind of like bow hunting. Get close and develop the load you want. They are very fun, and can become your primary range shooter.