You might find this hard to believe, but I own a .444 Marlin.
The .444 Marlin is a fine cartridge in it's own right. If you already own one or are getting a smoking deal on one, go for it. They will easily take any game animal on this continent.
HOWEVER......if you are looking at a brand new rifle that you are going to order and pay full price for, the .45/70 is the way to go. It will do everything the .444 Marlin will do and more. Good bullets are also easier to find. Also, if you don't handload, you are pretty limited with the .444. Good bullets are available. Monster loads are available. But, it is just a little more rare than the .45/70.