What is the best round ball caliber for Hunting?

[Skinny Shooter]

75cal. Brown Bess.
One shot on a doe behind the shoulder at 29 paces. Knocked her down.
Then she tried to get back up. She was dead and didn't know it.

Also have a .54cal Pennsylvania Longrifle (early Lancaster County style) which has only been blooded on groundhogs so far.
Am not too worried with my choice of calibers. Just gotta place them in the right spot.