Ah... This is hard. Well, I suppose one of the Satalin sisters for the sake of a tailjob(always wondered how that would feel), and Lala seems to be the most legal, so I'll go with that.
all I know is that I wouldn't choose the one with the green hair. Not that she isn't attractive. I would just be worried about her sneezing in the middle of an orgasm... though I suppose that has been solved as of chapter nine of darkness