Depends on which category. LeMat Revolver is the best Revolver in my opinion, and it's all a matter of preference. For stopping power - the Buffalo Rifle, however only holds one shot before reload. The Evans repeater holds 22 shots before needing to be reloaded and has considerable strength. Carcano is the best sniper rifle in comparison to the other, Rolling Block.
Again, this is a matter of preference you will have to find out yourself.