Im going with Ariel because she got what she wanted (to become human) and marry her one true love Eric. Also Belle's changed too because she felt odd in the beginning by not having any friends or marrying a handsome prince but hey she got the Beast who is one sexy god.

Ariel's changed alot and more than every one else.she has changes from mermaid 2 human,she has lost her voice and got it back again.even in ''the little mermaid 2''she changed again.

Not only did she change physically but she grew mentally too.
Then I would say Cinderella

i'm going with ariel, then cinderella, then pocahontas

Then Ariel, then Snow White.

or Cinderella:)

From nothing to everything :) Also Ariel

From a peasent to a Princes

Also Cinderella,Ariel and Belle.

If it was a new pick I would definitely choose Rapunzel, because her life changed entirely not only in terms of life style - leaving her tower where she spent her whole life hidden and isolated from people - but also on emotional level because she recovered from a Stockholm syndrom that she used to have because of Gothel and worked through her fears and insecurities, starting a new, adult life as a princess, growing out of her naivety and having a boyfriend whom she later married.

But with the given options I have to go with Ariel, because she went through all the kinds of changes: physical (turning human from a mermaid), emotional (changing a place to live and starting a new life in a world completely different from the one she was born and raised in) and finally, developing a trustful relationship with her father who ended up accepting her choices and wishes (something she never thought was going to happen, because the misunderstanding between her and Triton was one of the main conflicts of her life) giving his blessing to her when it comes to becoming a human and being with Eric.