Best? Ans. = 45/70. The 444Marlin is good, but suffers from lack of good bullets in factory loads. The 450Marlin is okay, but IMO not as flexible as the old 45/70Gov.
I'd skip the guide model, and get the 1895 with 22" barrel. IMO, the 18" barrel of the guide model is too short.
Take the full size gun with pistol grip stock. If it were me, I'd have a 'smith cut/recrown
the barrel to 20", and remount the front sight. Order a replacement front bead from
Williams, a white bead. Replace the rear sight, also from Williams, using a shallow V blade. It's a very fast and accurate combo. For a scope, check out a Weaver 1-3x.
It's inexpensive, but a great scope for the 45/70, and the ranges it's normally used at.

You can find a good selection of ammo at MidwayUSA. Following are some links for
the items mentioned.
Links:

MidwayUSA: http://www.midwayusa.com/

Scopes: http://www.riflescopes.com/store/default.asp

Williams: http://www.williamsgunsight.com/

ps: Just checked Midway, and the Weaver 1-3x scope is on sale for $129.99