Neither is "more accurate."
I have a gun that likes either, depending on powder charge. Also depending on patch thickness and ball size. The gun does not like tightly patched loads. It likes a loading with the ball sandwiched between wads even better though.
Smoothbores are all about load development (and maybe a little magic sprinkled with luck) with a willingness and ability to throw out the conventional wisdom of rifle loads.
I agree with
@Flint62Smoothie that a patched load should be the easiest to tune,,, but,,,, bear in mind what I said above about being willing to throw out rifle load conventional wisdom.
The biggest problem I would see with tuning a paper cartridge roundball load is consistency of bore conditions. A lubed patch, or a combination of lubed wad, with a tight fitting card in the mix somewhere,,, should keep bore conditions fairly consistent. I'm not sure a paper cartridge can do this. I would think (and very well could be wrong) that the fouling conditions of the bore will change a lot from shot to shot,,, mostly just getting worse,,, affecting the fit of your cartridge.