If you don't handload, IMO the best choice is the .45-70.
That being said, how many different loads do you need ? With the .45-70 you can shoot a huge range of bullet weights from a wide variety of manufacturers. I think you can even get lightly loaded "cowboy" ammo. But seriously, how many people really have a need to play around with all these different loads ? How many people can even find all these different loads to buy ? How many people THAT DON'T HANDLOAD ever really play around with these different loads ?
The versitility is nice, options are always nice but I doubt if very many people need this option. IMO, you give up nothing with the .45/70 while the other two have limitations.
As a general rule, the .444 Marlin shoots lighter bullets, faster, than the .45-70. Again, as a general rule the .45-70 picks up where the .444 Marlin leaves off. Basically the .444 Marlin starts with 180 grain bullets and ends with 300 grain bullets. The .45-70 will start at 300 and go up to 510 grain bullets. I REALIZE there are exceptions to all this: lighter, heavier, faster, slower: that is why I said AS A GENERAL RULE.
The .444 Marlin gets a lot of bad press on these boards due to posts that are incorrect. The .444 Marlin is not limited to pistol bullets, nor is the .444 Marlin limited to one factory load.