As for "companion" guns, I'm a 45LC guy. It took me a few years of trial 'n error to get there though.
Tried a 44Mag Marlin '94 way back when. What I found was that the one I bought kicked perty-hard with factory ammo, and that it wasn't all that accurate, nor reliable. In fact, the Ruger SBH that I was using at the time was capable of better accuracy than the Marlin. Thing about the SBH though, was that it kicked even harder and was such a big ungainly revolver that it was plumb-unhandy to pack around.....and not much fun to shoot, leastways not for me.
Enter the 45LC. It still has a big fat bullet, is still quite accurate, and is available in a smaller/handier revolver. I've also found that even in it's standard "service" loadings, the 45LC has much more power than it's paper-ballistics suggest. The recoil of a 255/850-900 load is more than managable out of a Colt-sized 6-gun and almost non-existant out of a levergun. One can litteraly shoot either all day long for fun, take all manner of deer and hogs, and/or use either as a defensive arm.
The 30-30 works good for me too. Adds about 75 yds of range over the 45LC out of a carbine, still fun to shoot and the rifles themselves are reliable....and perty cheap.
The 45-70?....Bigger/heavier gun, kicks real hard, ammo is rather expensive, dies are rather expensive, and the guns are rather expensive. I've shot a few 45-70's and must admit that they have a certain charm. But being's how I don't plan to be tracking down big bears or elephants, or engaging in long range competitions, I never saw a thing they would do in the woods that a good shooter with a 30-30 can't do.
All that said though....was I starting out new today, I might just lean towards a 357 combo, or maybe a 38-40. Both of those have an out-of-porportionate amount of power out of a light/handy carbine too. And aint bad out of a 6-gun.
Just my 02 .
DGW