underweight, skinny girls aren't my type really, so I'd go with the slightly overweight girl. that said, weight isn't high up the list of priorities and there is probably something more important than their dress size to use to pick between them.
well my girl is probably around 10-15 lbs overweight but she is 5'11 so that's not too bad. I actually prefer her to have a bit of a belly I think it cute. id her b a little overweight then under or fit actually. plus most of it is in her butt