If i had to pick, 3. I dont think any of these dresses especially 1, 2 and 4 are flattering at all because they're far too low cut!! No matter how busty you are the style of the dress is so low cut it goes past your boobs and just looks ridiculous in my opinion.
For a ball you have to make a choice that will be slightly different to what most say. Don't forget practicality, durability and warmth are going to be issues.
On that basis I'd say;
2. May be a bit cold, fabulous if you've the the accessories to pull it off but hard to match stuff too, possibly a bit stand-out. Bright colours are ok though at summer balls.
1. Too much length and loose material, horrendous for walking round a ball in. Definite no.
3. White is potentially a bad idea, may get noticeably dirty. Otherwise a reasonable choice, the shape is certainly good.
4. This one is good, easier to pull off than 2), but I'm not quite sure about the shape of it - makes the models curves look flat.
I'd not like to see a girl in 1), the others are all nice. Don't forget that different colours suite different skin tones - white is a bad idea for pale skin tones, black goes best with dark hair etc. that said shape is the most important thing.