I have both calibers in Marlins. Three 1895's (1895CB, 1895GS and 1895) and one 1894CB in 45 colt.
I'd HATE to have to pick just one or the other and don't know that I can give you an answer but I can list what I like about each.
The 1894 Cowboy Limited is absolutely one of my favorite rifles. It cycles everything I've loaded including over-length Keith style SWC cartridges. It shoots Jacketed and cast (both commercial and home brewed) bullets very well,
http://www.grovestreet.com/jsp/onepic.jsp?id=1225592 . It does seem to prefer bullets 250 grains and higher, loves 320 gr cast bullets. The 1894 is slightly easier to clean than the 1895. I have over a week in the field with it this year. It carries great and is easy to shoot from field positions. The 45 Colt is an easy cartridge to reload, 99% of what I shoot out of it is at the Colt replica max or just into "Ruger/Contender Level" loads. Even the hot stuff is easy on the shoulder. Knowing that a 300 grain bullet out of 44 mag out of a revolver at 1200 fps will easily pass through and Elk (east to west anyway) I'd even use this rifle with the 320 grain wide meplat cast bullet traveling 1300fps + (= to factory 45-70 300grain loads) on a broadside Elk inside of 100 yards. Anesthetically and ergonomically perfect IMO.
I've also hunted and shot the 1895's a good deal the last couple of years. The accuracy is slightly better than the 1894's and I'd feel more comfortable shooting at bigger game and at longer range with the 45-70.
http://www.grovestreet.com/jsp/onepic.jsp?id=1206746 The GS is easy to carry in the field and has proven to be devastating on game. It took a Idaho Bear this spring and all who witnessed were impressed by its lethality. The bullet, 425gr Bearthooth Pile Driver Jr, jogging along at around 1400 fps took the long way through the bear, front left, to right rear busted through everything along the way and was last seen heading toward Montana. The Bear had a thumb sized wound channel all the way through... He expired before he could even think about skedattiling.
The 45-70 cartridge is easy to load though components are more expensive. I cast Ranch Dog's excellent 420gr bullet and a pound of lead only yeilds 16 of those beauties. I don't typically plink with my 45-70 but a 405 cast bullet over 11 grains of Red Dot spits out of the barrel at just over 1000 fps and is 3" accurate at 100 yards. Its a good load to introduce new big bore shooters with.
If big heavy bullets going fast is appealing to you the 45-70 levergun is capable. It takes a chronograph to appreciate them unless massive recoil is what you are after. For me the fun ends about 1800 fps with 400 grain bullets. The gun is capable of more but I find no pleasure above that.
Most factory stuff is mild but effective. The LeverEvolution ammo expands the versatility for non-handloaders.
Both calibers would be among the last I'd get rid of...