IMO, the Cowboy seems to recoil more because it has a little more drop to the stock than does either the Guide Gun or the Sporter.
Stock shape/design has a lot more to do with perceived recoil than most think.
If you're gonna hunt North America with a .45-70, with the exception of the big bears, dropping down to either the 300 or 350 grain slugs will work wonders (at both ends) with a gun of any weight.
The Cowboy and the Guide Gun are both extremes - both of which I've owned, hunted with, and subsequently sold.
As posted above, the best one is like Confucious say: balance - I'm very happy with a 22" Sporter, which I'm thinking of swapping out the PG stock, etc, for a Guide Gun butt/lever/etc, and shortening the mag to a button mag.