To be honest the cut of the black/blue dress doesn't fit your body as well as the cut on the floral dress does and you want something that is going to accentuate what you've got to show. I say take the floral dress, get a nice sash like thing, a braclet, necklace, earrings and some shoes and you could throw a very nice looking outfit together, but the pink is too bright and the sparkly is too clubbin for prom....