Hmm... Elsa. I don't say this because of all the Frozen hype. It's not even my favorite Disney Princess movie and that's not because I don't love it, but I have ones I love more. I love Elsa, though, because she's just so relatable. Her and Anna apply to my life so much. Elsa went through a period of isolation and it distanced her from her sister. The whole movie is like my life story in a way with my sister. We have a somewhat strained relationship because of my depression and this movie really opened up my eyes to how I need to change so I don't regret not being there for and with my sister. Mulan is next.
Although he is a rich prince with tons of servants and a big sexy castle lol, his personality flaws and internal struggles to overcome them actually make him quite relatable as a person; he is someone you can cheer for as he struggles to overcome his temper, self-doubt, despair, impatience, etc. in order to get the girl.
Besides, it's badass for a character to run around shirtless -- with a cape. xDDD