I like the .44-40 and have several rifles and revolvers which use that cartridge. However, unless you already own a .44-40 rifle and/or revolver, the .44 Magnum is a better choice. The .44-40 is really a handload-only proposition, due to the expense and scarcity of factory loads. You must also be aware that only the Ruger Vaquero, Davidson's Super .44 Blackhawk Convertible with dual-cylinders, and the S&W Model 544 Texas Wagon Train Commemorative of 1986 are strong enough to handle heavy .44-40 handloads up to 23,500 psi suitable for the Winchester 1892 rifle, about 1200 fps revolver and 1700 fps rifle with 200-grain bullet.
In older Colt revolvers, the Winchester 1873 rifles and their modern Italian clones you are limited to loads not exceeding about 14,000 psi, similar to factory ammo, producing about 900 fps revolver and 1200 fps carbine with 200-grain bullet.