Where to start.
The 45-70 was the second cartridge ever officially adopted by the US Army. It's been around since 1873s. It's originally designed for black powder, it has huge case capacity for smokeless loads. With a Ruger #1 or a Winchester highwall it can be loaded to slobberknoker-retina separating levels. And if you get one you need to do that once and get over it. (350s at 2400FPS from a 24" barrel in an 8 lb rifle) All of the big 45s are 200 yards and in rifles. Yea, you can shoot them to 1000 yards, and BPCR shooters do it with black powder, but look at the drop on any of the 458 cal bullets at any speed you can reasonably hold onto. The bullet drops between 18 and 21 inches from 100 to 200 yards.
I own two 45-70s, a modern Winchester Highwall with a 24" barrel and a C. Sharps '74 with a 30" that only gets fed Holy Black and galena. I like my single shots.
In a lever gun you can get into a 45-70 in a guide gun, or a 450 Marlin. The 450 Marlin duplicates the 45-70 in a modern rimless case that is a little shorter. That is not a problem, the 45-70 is way to much capacity for smokeless powder.
In factory loads for the 45-70 you have to mind what you are buying. Many of the loads out there are designed to be safe in the trapdoor Springfields that are still around. The 450 Marlin is only out there is real world 21st century loads.
I like the 45-70, I own two and love loading for them. I have a buddy who shoots a 450 Marlin and doesn't reload. If you are not planning to get too into reloading I'd get a 450 Marlin. It hits deer (and one coyote that I know of) like Thor's hammer, ammo is available off the shelf that works.
The 450 Bushmaster is a .452 as opposed to a 458 for the cartridges above and as such uses pistol bullets. Anything with a .458 bore gives a larger selection of rifle bullets.
Ignore the posts about the 458SOCOM, it's not a straight walled cartridge.