About four years ago I was trying to decide between the three calipers and ended up with the Marlin 45/70 (with a 22" barrel; I personally don't care for the 18" version) because of the ammo availability. I agree with Jeff in the fact that the .444 is an oversized .44 mag and is someone of an oddball (IMHO)......Not sure about the availability of ammo for the .444 but my guess is that it's very limited.
The .450 is nothing short of a block buster and I'm sure it will rattle your fillings when your shooting it. I've seen .450 shells where I have bought my 45/70, but you don't have the variety like you will find with the 45/70.
Anyway you look at it, the shells are going to be a premium. I don't recall how much I paid for my last box of shells for the 45/70 but it was $25/$30 range. Regarding the "hot" 45/70, I've shot Hornady's LEVERevolution and all I can say is that it kicks like a F'ing mule! Not sure how the ballistics compare to the .450 but it has to be very similar.
Like I said before, I bought my 45/70 four years ago and I haven't second guessed my decision once.
If you want to see the ballistics for Horady's 45/70, take a look at this link:
https://www.hornady.com/shop/?ps_session=59c4f5e5174480f7aacac919f4e5a4e2&page=shop%2Fbrowse&category_id=e2efc3a895f8f6004aa5509977a8de6e