Bullseye and Power Pistol have the highest energy per unit charge weight for any of the powders listed in QuicikLOAD's database. Due to flake size, Power Pistol has the higher energy per unit volume.
However, because many of the ball powders settle more compactly than flake or extruded powers, there are many ball powders that have higher energy per unit volume than Bullseye or Power Pistol. For example, Win-296 exceeds both.
I did not do the math to compare all of the ball powders, but I expect that Win-296 should be near the max on the basis of energy per unit volume.