I'd nail all three. Anything larger than the right chick is a bit much, but anything up until that point is fair game imo.
The only good thing about skinny bitches is that they are easy to lift. If you get thirsty while laying pipe, you can just run to the fridge and take her with you without missing a stroke.
1: pussy only
2: both
3: ass only
I would not do anal with #3, because you know with a healthy appetite like that, her colon would be full. I don't like skidmarks.