Smokeless powder comes in three forms.
Single base: nitrocellulose
Double base: nitrocellulose plus nitroglycerin or nitroguanidine
Triple base: nitrocellulose, nitroglycerin, nitroguanidine.
The remainder of ingredients are stabilizers/preservatives (aryls/phenols), flash retardents (calcium carbonate), plasticizers/binders (such as polyester), burn rate modifiers, coatings (graphite).
So whatever powder is the most pure triple base powder would have the most energy per unit of mass. How that stacks up mass to volume has a lot to do with the shape of the final product (flake, stick, ball, squished stick, short cut stick).