For caliber, my vote is for the .45-70 unless you just want a new chambering. You'll save $ on new dies, brass, etc., and factory ammo, while anemic, is readily available if ever needed. Nothing the new .450 Marlin can do that a handloaded .45-70 can't.
The Marlin 1895s are great, but I don't care for the Guide Guns due to the blast enhancers at the end of the barrels. Lots of people in agreement on that one. Better a regular 1895 cut back. My .45-70 lever gun is an older straight-stock, short barrel, 1895 Marlin without the saftey and blast enhancers, and I love it. Carried it in the off season when I lived in Alaska and it's my repel boarders weapon here at home now.
I really like the Winchester 1886 in .45-70. too. Would cut the barrel to 18 1/2" or 20" though. Maybe some day.
Rocky