Most Helpful Guy
You should use the largest one for a new one. That way as it gets older and loses elasticity, you can tighten it.
Most Helpful Girl
It depends on the brand, shape, fit, and comfort level. I have a pretty big bust that doesn't stop growing, and im 25!!! So i find a bra that will fit comfortably with the shape i like that will clasp on the tightest and as i start to grow out of the bra i move the clasp each time, i also buy bras with 4 clasps going down, and 4 clasp options. But like i said it all depends on comfort level!!!