Tina
Let's not lose sight of the fact that Bill Rataczak said publicly that Tina was "the brains of the outfit," and he bought her a bottle of Chanel#5 on behalf of the whole cockpit crew for saving their bacon. His note to Tina on the perfume said: "The guys in the front of the plane are here today because of what you did," or words to that effect.
To me, Tina had a level of comfort and savvy with DBC that Florence did not. Plus, Tina stayed with Cooper for up to five hours, 45 minutes of which she was alone with him, and she didn't loose her cool. In addition, Tina looks very comfortable and articulate in front of the cameras after the hijacking.
Yet, to me these behaviors are in striking contrast to the woman she became. For me, the question is why.