Hmm.. kudos, interesting way to cap off the night. I actually think the girl 2nd from the right is kinda cute, it might just be not optimal lighting, perhaps with a bit more makeup, etc. In my view the far left girl is easily the most unattractive one.
Now then as to the answer, mind you I don't regard the situation this way, but knowing how the bulk of society thinks (unfortunately)... I get the feeling just from the hang of her clothes that the 2nd from the right is perhaps the "heaviest" of the bunch, but that of course doesn't mean she's even at all "fat", just that in the context of these 4 girls, she's the thickest. I don't think there's anything wrong with her at all, I definitely wouldn't call her fat, but most guys seem to have an extremely low tolerance for "extra weight" on a girl (and after all, because most guys are incredible looking Boflex models...
) and so there'd be a bunch who I'm guessing would regard her as possibly fat, and as such, she'd be the one who'd theoretically have to put out more to have her fun.
Hence, she's the whore.
and errm... what's her number... ?