"Best" is a slippery word.
The 30-30 is better if getting ammo easily is of high concern.

The 303 is more powerful, and more versatile.

The 34-40 Krag is good too, being between the 30-30 and the 303.

The 30 Russian is the best of them all in a 30 cal, but harder to get reloadable brass for, and you need a strong action if you make a double in this caliber because it's running higher pressure then the others and had more volume too.

Any of these are going to have pros and cons that vary depending on the use of reloaded ammo,vs Factory ammo.

So what is "best" depends of the "mission" the rifle is being called on to perform.

If I were building a double rifle that was ONLY going to be used for deer hunting, and ONLY used in areas where shots would be under 175 yards, I would probably go with the 30-30. I would use handloaded ammo with 150 grain spitzers in that rifle, and regulate it for that load.

If I were going to use in for a broader cross section of my hunting, I would go with the 303, with 180 grain bullets, or maybe the 7.62X54R with 220 grain bullets (made on two .308” bore barrels)