Ballistic studies are always enjoyable and there is plenty to learn if you approach things with an open mind.
Whenever you put the word "Best" into any discussion, it helps to narrow things down to not only specify game species, but what type of shot, ie Elephant brain vs body shots.
The .375 H&H is always going to be a favorite for Dangerous Game, and easily the best all around cartridge for hunting Africa, but would not be the first choice of many on this forum for body shots on Elephant.
Another factor mentioned by
@Mark A Ouellette is the particular bullet used. When manufacturers design a bullet, they often have no idea what cartridge it will be loaded in, what game will be hunted, at what distances, or any other factor that will effect it's performance. In the .308 dia., factories tend to use 30-06 velocities a baseline for designing that caliber. Their Premium 150 grain bullet may be used by handloaders in a 14in 30-30 T/C Contender pistol, or a 26in 300RUM, yet customers will expect equal performance from both.
Selecting the "Best" should obviously start with the species being hunted, then the recoil that particular hunter is capable of shooting accurately, then the bullet most suitable for that game under conditions of that hunt if possible.