.44-40 would be the classic choice.
.44 Mag would be a good choice as well, easy to load, and there's a good selection of rifles available. It's not a "classic" caliber, but brass is easy to get, and it's forgiving in the press. It will not seal off the chamber for cleaning as well as .44-40 for BP use, but... it's still a good choice. Do you plan to load smokeless or BP? If you are in the smokeless side of things then this would be my first choice. If you are going to load mostly BP then I'd pick .44-40.
Last edited by Willie Sutton; September 6, 2012 at 07:59 PM.