Princess Fiona is the lead female character from the Shrek franchise. When she was a child, she was locked away in a dragon-guarded tower by her parents, King Harold and Queen Lillian, because of a terrible curse: Fiona transformed into a hideous ogre at night! The curse was broken when she shared "true love's first kiss" with Shrek, and now she remains a beautiful ogre forever.
My vote goes to Cameron Diaz, as she is the original. Holly does a pretty spot-on impression of Diaz's performance, and Renee was obviously chosen more for her singing ability than sounding like Diaz. All three are great, but Cameron is stealing my vote on this one.