As to the question from the OP, we can't really say one way or the other what would be better, since there has not been a study on the nutrition of ball pythons or other snakes.

Even to that, we couldnt say for sure if the fat content is an instrumental advantage or disadvantage for snakes in captivity. Could we speculate that breeding females do better with a fattier source of food than males do? Or can we assume that since the fatty deposits are inside the body, pressing against organs, that all snakes would benefit from a leaner prey? In general, snakes in captivity are much fatter than their wild counterparts.

At this point in time, I think I'd rather assume I know little of the physiology of my captive snakes to pointedly say a leaner meal is always better.