I've loved Ariel since I was 3. It probobly had to with my red-brown hair, and the memories I have of meeting her in WDW. I sat there for at least 8 minutes blabbering away.
Kairi is now one of my faves. She's not part of the Disney Princess franchise, but she is a Princess of Heart (like Kilala). Same with Alice. Why's Alice a Princess of Heart, anyways?
Princesses of Heart are women/girls of pure light in their hearts. There is absolutely no darkness to be found, so much so that even if there is an attempt to turn them into Heartless, it wouldn't work because of the complete lack of darkness.
Alice is pure of heart, the perfect candidate for being a Princess of Heart. It doesn't mean she has to be of royal blood though; it has nothing to do with that. People seem to forget that they aren't all royalty to one specific kingdom, rather than their selflessness and kindness, etc. makes them alike to royalty, hence the name Princesses of Heart.
Why Ariel isn't a Princess of Heart is that she sided with darkness to get what she wanted (in this case, using Ursula, a known evil, to get feet/defy her father and give Ursula the trident).
That and you wouldn't be able to play with her in Atlantica, haha!
Belle would definitely be mine because she is one of the very few whose story wasn't centered around her chasing after a prince. She took the spot in Beast's castle so her father could be free...that is just amazing right there. haha
Also...I'm doing this musical right now so I've been learning a lot about the real meaning of it xD