the 450 marlin is awesome by far out performs the 45-70 ten to one. But the 450 marlin is one of those cartridges that just doesnt really have its place in the shooting community kinda like the 454 casull there still around just not as popular anymore as when they first come out. The 45-70 has been around for over 100 years has made its name and is here to stay.
I would have to go with a 45-70 not to mention more of an abundence of case availability and bullet varieties , and many more varieties of factory ammo.