Whitewell would surely win! Cause she seems more powerful to me than Nat, who seems to depend a lot on Bartimaeus to get him out of trouble. He managed to reach his career's pinnacle mainly due to Barti's efforts. Jessica on the other hand, does'nt seem to wholly rely on her demon's powers to get out of trouble or achieve something. Plus lets not forget Nat's initial failure with the Staff. I feel strongly, Jessica might have succeeded there. Also, she was'nt completely corrupt like the other bastard magicians. Nat might have remained corrupt & gone worse, if not for Lutyens & Kitty's guidance.
And off-topic, I don't think Ginny & Kitty are Mary-Sue's.
"If the bee disappears from the surface of the earth, man would have no more than four years to live. No more bees, no more pollination ... no more men!" - Einstein
"I like quoting Einstein. Know why? Because nobody dares contradict you." - Studs Terkel.
<@Ximenez> Sentynel: But i have a life? No. Qed.