Both of the models you listed have "ballard rifleing" . This is what you want and will handle both jacketed and cast. If you are considering a used gun be carefull to avoid "micro-grove" as this type of barrel isn't a great performer with cast bullets.
The 38/357 will handle all kinds of cheep ammo and is cool for blasting and general shooting fun,great for protection against 2 leg type varmints . Could also be pressed into service in shtf for close range hunting up to medium size deer.
The 44 is going to be a bit more expensive to buy ammo for if you do a lot of blasting,you really want to learn how to handload,44 is easy to learn on and will save you the most per shell on a factory vs handload type of cost check.The 44 in a rifle is an excelent hunting round at close to medium ranges on up to medium size game, the 44 out of a longer rifle barrel really cooks compared to a pistol. The 44 with full power heavy bullet loads will make you pay attention but compared to most any rifle bigger than a 223 it isn't any big deal .
Both the 357 and the 44 out of a rifle are heavy bullets going at a moderate speed when compared to most rifle loads so the trajectory is somewhat rainbow shaped. To place a scope on one of these is kind of overkill and makes a fine handy rifle kind of heavy and out of proportition. The factory sights are somewhat slow and downright difficult for my 50 year old eyes. The solutition to this delema is a receiver mounted peep sight. The marlins (and most modern lever guns) are all drilled and tapped for these sights so it is a matter of buying a sight from midway or brownells and getting out your screwdriver set.
The peep is fast and easy to use,it solves many eyeball problems ,it is cheeper than all but the junkier scopes (remember you will need both a scope and some type of mount and rings) and is more durrable than all but the highest dollar scope and mount system .
I think the marlins are some of the best lever guns,I have the 44 in the cowboy rifle (heavy octagon barrel) and put a tang mounted peep on it . This sight looks right on this gun but truthfully the receiver mounted one is a better sight because the tang mounted model can limit the way you grip the gun and tends to "fold" at the worst times . I really only use this gun as a range toy so it is all fine,your choice is a much better all around gun .
I have a yearning for the full size 45/70 marlin (you can keep the guide gun,I have shot a couple with fairly hot handloads and didn't much care for it) but the budget never meshed up with finding one .
I might get a little cash from a car crash(some missed work,some trips to dr officies,odds and ends I have allready written off or paid for out of pocket) and I am thinking of an ar10 type or the marlin. It things work out well possibly both! Truth be I would shoot the marlin more than the ar10.
Both your choices are fine,lean towards the 44 if you think you will hunt,spend the $40-$70 for the peep before you spend a bunch for mount,rings,and scope. (you will spend more for the rings and mount than for the whole peep sight!) Prepare to have bunches of fun!