With roundballs compared to roundballs, the .54 should be hands down more powerful. The .54 ball is .530 - .535 inch diameter and weighs 230 grains (.535 diameter) compared to the .50's .490 - .495 @ 177 grains.
Load each with 80 grains of 2F Goex
The .50 makes 1,694 fps, and 1,128 ft/lbs
The .54 makes 1,487 fps, and 1,130 ft/lbs
So it comes down to other things when it is time to choose. The larger bore tends to be more forgiving. With properly designed and executed rifling there is more room for fouling to build up and not interfere with the following shot(s) The larger ball makes ba larger hole, and, due to having more material, can expand to a larger diameter inside the target. Either way there is more internal damage and the animal dies quickly. If a marginal hit is made on the animal, the larger wound channel can make a big difference.
With paper targets, or the old game of shooting charcoal bricquetes hung on a string, the larger ball is easier to score a hit with.
Neither one is a bad choice. I cannot feel the difference in recoil between the two with hunting loads.