I'd go for the athletic figure. I think that suits Rainbow Dash a lot better then an hour-glass shape with big boobs and broad hips.
For an athletic figure the bust and hip's should be about the same width. Say, if the bust is about 80 cm, the hips should be about 80 cm too. And the waist maybe 65 cm. That would give you a column body shape, which I think is the most common body shape for athletic women. I have a very athletic figure, and my measurements are 84-63-86, and I'm 172 cm tall. I hope this helps somewhat.. ^^