It's been awhile since I last saw Beauty and the Beast so I can't remember if she becomes a princess or a noble woman, but Disney always calls their favorite heroines princess.
Anyhow Belle is my favorite. Unlike the other princesses she seemed more interested in books and knowledge, was content with her life, and loved her father. She didn't want to be with and marry the handsome rich guy of the town (and spend her time in the kitchen barefoot and pregnant as he wanted her to be) like all of the other princesses tend to do but instead sacrificed herself in place of her father to live with a short tempered, rude, and selfish, scary beast who was a beast throughout most of the movie and fell in love with him despite his looks and after a drastic attitude change.
Belle seemed like the opposite of all of the other Princesses except for the recent Princess and the Frog story. That seems the same formula wise except for the antagonist.
Since I am her through and through, Belle. She is pretty much exactly like me. I also really love Mulan. She isn't considered by most to be a Disney Princess but to me she is. She is so strong and honorable. She fought for what she wanted and believed in.