Clair, hands down. She is the definition of "sore loser" and doesn't deserve her position on account of how self-centered she really is.
Although Whitney cried over her loss like any stereotypical pretty girl would, she still honored her Leader position and gave out the Badge like a good sport once she calmed down.
In comparison, Clair spat on you for beating her and sent you to take a test with the elder instead. Afterwards, the first thing she asked you afterwards is if you failed, and then she still refused to give out the Badge. It's only when the elder threatened to tell Lance on her that she finally conceded defeat.