None of those 3 (4 including the 375) are a wrong answer, but I personally opine the 45-70 to have the upper hand. The .450 Marlin is what a modern 45-80 should be, in terms of power, but it’s not as popular, and typically I have seen more “Marlin only” .45-70 factory loads on the shelf than I have 450 Marlin loads. For hunting whitetails, SAAMI compliant, low pressure standard .45-70 ammo will do whatever you could need of it, with lower recoil and lower cost. So the 450 matches the top end capabilities, without the common availability of low end, practice ammo.

And of course, it ain’t a .45-70.

The 444 Marlin is a cartridge I really want to love, but tend to come up short. I’m about as big of fan of .44 mag as anyone, and ~15-20yrs ago when I was pushing Marlin 1894s with little 44mag cases to their max, the 444marlin was a welcomed option. Less recoil and less powder than the Marlin only 45-70 loads (very similar recoil comparing SAAMI loads in similar weights), but less factory ammo and brass availability, less bullet weight, and less viable 44cal bullets available. Without my own 44-ophilia, I can’t say I think there’s any reason to grab a 444 over a 44mag unless you were a dedicated hardcast bulletmaker who wanted to port the same pills in your rifle as your revolver. I suppose a guy could almost make a case to support the 444 Marin is a unique combination of less recoil, less powder, less lead, but the same effective range on the same game in the field. Almost.

But, of course, it ain’t a .45-70.

Almost arbitrarily, I like the 444 more than the 450, just for my bias for all things 44 cal, but given the 3 standing beside each other in the rack, and enjoying dating all of the above, the .45-70 is the one I’d marry if I could only pick one.

In a Marlin levergun, I’m not sure I’d venture farther than those 3 options, and I know I’d personally land on a 45-70 1895. There are a handful of other chamberings out there in the Marlin, including the .375 Winchester and the chamber-mate .38-55, or the more modernized 35 rem (a hunter’s combination if there ever was one).

Might be worth your while to dig around for a Marlin in .375 win to compliment the old Savage, and better justify the ammunition supply on hand. Looks like there are a couple on Gunbroker at relatively reasonable prices right now.