an interesting question... although i am loathe to restrict to one-of-this or one-of-that (would you hold a carpenter to one saw or one hammer, a plumber to one wrench?) i would posit the following:
(to quote my son-in-law, a second year law student) "It depends"
primarily on the rate of twist of your rifle. As a general rule, if you are trying to stabilise a heavier projectile, you need to spin it more quickly as it goes through the air. Therefore, your rate of twist to keep a maxiball or similar conical projectile stable in flight will be much faster than the RoT of a gun designed to shoot PRB. The MaxiBall was, if i remember correctly, developed by Thompson Center, designed to be fired through their Hawken- like rifle. (I still have the Renegade which i bought back in the early eighties ... it still shoots straighter than i can hold it.) This design sports a 1:48 twist, that is, one revolution in 48 inches. This was a compromise, so their barrels could shoot both PRB and their conical MaxiBall. Some hunters would simply not be convinced of the potency of a PRB, and thus the marketing gurus at T/C won out and the 1:48 barrels hit the market. Later on, "roundball barrels" became available - i think they have about a 1:60 rate of twist. While it's on the list, i've yet to try one out.
I will confess that i have never tried the MaxiBall in any of my T/C rifles. (By the way, the grooves are a bit shallower than one would find in a barrel designed for PRB, but that's for another time.) I am told that the accuracy is pretty good with the MaxiBall, but i've never felt the need to try it out.
So
if this is a once-in-a-lifetime hunt, and you're having a rifle built to that specific purpose, i would recommend a fast twist barrel with slightly shallower grooves set up for conicals. This will set you back some pretty serious coin. You may want to contact Charles Burton at FCI barrels, or Bobby Hoyt. Then you will need to determine which weight of conical will give you the best performance. (I assume that you are working with a .54 caliber gun here - i would be hesitant to hunt anything bigger than white tail with a .50.)
If, on the other hand, you are going to be able to hunt
big game on a more routine basis, you would probably want to stick with a .54 rifle using PRB. Use Dutch Schoultz' method to get the best accuracy.
Hope this helps. There you go: free advice and doubtless well worth the cost.
Good luck with your project, and good luck with your hunt.
Make Good Smoke