Robin would have the edge in terms of looks, though Nami looks good in her own right.
However, dunno if it's an unpopular opinion, but Robin's character post TS is ass. She feels like an NPC unlike Nami, who I feel like has a more substantial role and more character depth. Her thoughts and emotions are more palpable.
So if I had to choose a relationship with one of their real life equivalents based on what we can judge, I'd go for Nami.