The 20 is symmetrical, so if you aim for the center, and are slightly off to the left or to the right, you are equally likely to still hit, compared to the 19 w

The 20 is symmetrical, so if you aim for the center, and are slightly off to the left or to the right, you are equally likely to still hit, compared to the 19 which is at an angle and thus biased to one side. Therefore, when shooting for the 19 you'd have to rotate your point of symmetry which means adjusting the angle, speed, AND left/right. I personally don't have any data to support this, but it seems extremely intuitive and so I think the burden should be on you to show 19 is equally easy to hit if for some reason you think it is. 20 also has the advantage of getting you closer to 0 if you don't shoot a perfect game, which is pretty much always, so 20 is BETTER unless 19 is significantly easier to hit.