Eri from School Rumble. She is one of the few examples of a tsundere character being portrayed as human rather than a walking cliche. She goes from a supporting character to a central character as the story dives further into her personality than probably anyone else. She's popular, yet insecure. She is aware that her sharp tongue is a negative but she can't seem to stop herself. It's a bad defense mechanism, one that sabotages relationships as a twisted way of protecting her heart. Just a fantastic character.
From the poll options, I pick Karen Kujou from Kiniro Mosaic. One of the most genuinely fun characters in all of anime.
Oh, and Girl Genius Kokoro-chan counts, too, doesn't she? I can't prove that she is mixed but she did graduate from Harvard (maybe).
