i've tried both, and i have tried different combonations of hole size in the waterfall and holes in the cap to regulate how much air and go through the cap before hitting the weed, and i found that a gravity bong done correctly will make a much more milkier and bigger hit, because you have controll over how much smoke is coming in so its just enough while a waterfall could have to little water going out and less smoke is coming in, or the hole is to big. In turn its the same phsyics but a gravity bong has more controll so in turn a better hit.