Sorry... but best at what? Nothing in any of the three films, (at least comes to mind), that Connie possess a natural feel for dealing with the Corleone's criminal affairs. In Part III, her sole drive as a character was to encourage Vincent to become Don, which is why we see her for the first time taking part in these sort of affairs.

Puzo's novel tells us Connie was very close to her father, a sort of "daddy's girl" if you will. I always thought Connie was helping Vincent, because not only did he remind her of her own father, ("You're the only one with my father's strength"), but she probably hoped Vincent's reign as Don would see a return to the glory days of when her father was in charge. Because then Connie would feel safe, as she did before her marriage to Carlo and when the Don was shot - when her world began to crumble. At least that's how I see it.

Now don't get me wrong, I love Talia Shire's portrayal as Connie in all the films, though personally I would find it unusual to see her as a consglerri, and suddenly playing a pivotal part in the Corleone criminal affairs.