Well it depends on whether you ever want to be able to just talk with your contacts and random NPCs in ways that don't involve massive tests but simply getting some social activity done. Negotiation is useful for shopping or bribing a bouncer, a few points (bought through karma most likely) of Etiquette can help when dealing with contacts, gangs, things like that. Con is for smoothtalking a security guard or a distrusting cop. So it depends on how socially inept you want to make your character.