I love the 45-70 round. It's capable, reliable, and dead simple. I have more fun shooting my 45-70's than any other rifles I own.
Here's a couple that sit in my safe right now:
This Remington made 1895GS is what got me hooked. Might be Remington, but the sights are straight and the action is quite smooth.
After shooting the guide gun I fell in love with the 1895 Cowboy and had to find one of those too
There's just something about those big .458 bullets that really speaks to me,
Of course, once the bug has bit you, you'll want more rifles that fire those big slugs so you'll have to venture out a little further. Maybe a bolt action?
The 458 win mag is basically a 45-90 with a belt instead of a rim
I only shoot cast bullets in the 45-70's. 390 to 450 grain. I load the 390's to 1900fps and the 450's for the Cowboy at 1450fps. I did a penetration test with water jugs and the 450gr went through 19 four liter jugs of water. I figure thats enough. When using cast bullets, hard-cast flat nose are excellent hunting bullets and do not need to expand to be effective. I have shot gophers, 2 coyotes, and one white tail with mine and haven't recovered any bullet, but death was swift and almost no meat damage.
I haven't killed anything with the 458WM yet, but I have various jacketed bullets for it from 300 to 500gr and I also plan to see how it handles cast.
Be careful as big-bores are a powerful addiction
I would not hesitate to buy a new Marlin. I have handled half a dozen in the last 4 months and all were acceptable and a few were very nice. All much better than 2-3 years ago.