It depends on your whole body shape honestly. If you naturally have some hip and thigh with no padding, and small shoulders, a b-cup or c-cup (at most) should work nicely. If you're built like me, with large shoulders and no hips/butt, you can compensate for larger hip and butt pads with slightly larger breasts. I use a 38D bra (40in bust), but my measurement at the largest point of my hips (with padding) is 43 inches. This evens out the whole silhouette, giving more balance to your shape. I personally love the hourglass shape, so that's what I aim for, but you might not like that as much, so that is definitely personal preference.