There are two Marlins that I don't think you can ever go wrong with:
1) The 39a in 22lr
2) The 1894c in 357
Both can be hard to find at times, although it seems that the supply is loosening up (e.g., 2 or 3 1894c's have been in the EE recently).
I really like my 1894c. The 18 1/2" barrel makes it a dream to carry and the 357 is both a cheap round to buy factory and a whole load of fun to reload (I like hurling 180gr cast out of mine).
I have a pretty good Marlin collection, but was missing a big bore. I just purchased a 444 --- there's something about owning a Marlin in a Marlin-labelled cartridge. But since you have already have a 45/70, I'd definitely put my vote in for the 1894c.
BTW I have a spare 39a of 1950's vintage in VG+ condition that I'm going to be listed in the EE this week.