I'm not sure about if I should include Rapunzel...
And I'm not sure about the answer either.. :)

Aurora
~Secretly a princess
~raised by fairies in a magical land
~gives in to Phillip's charm easily
~loves all animals
~both parents living
~animal best friends

Tiana
~not born a princess
~raised in New Orleans by humans
~resisted Naveen for quite some time
~never liked frogs much, and I'm sure Lewis is the only gator she likes
~father is dead
~human best friend

Doesn't get too much more opposite than that...

^Good points! Well, also Tiana isn't that romantic..

Which is probably why Ariel's my favorite and Aurora's my least favorite

ariel? no way, they're not that different

agree with firegirl1515

...she's not that different from ariel.

The only thing they have in common is that they fell in love with a handsome stranger other than that I can't think of a darn thing they have in common

^^They're both dreamers. They both have pink dresses as a lineup version. They both have female villains with strange colored skin who use them as a means to get back at their parents. They're both born princesses. They're both known for having a lovely voice. They both have animal friends. Their princes don't know that they are princesses when they first meet them. Thy are both seemingly going to be denied their true love. They both look a lot like their mothers.

...any other similarities I missed?

^well a little similarity that Ariel has Sebastian besides her dad who controls her, and Aurora has fairies who look after her too. They all are strict but kind.

they're dreamers, they fall in love at first sight, they're both somewhat girly, they're both curious....
......
I think, Kataralover, you just like to think they're so different because Aurora is your least favorite.

or Ariel

or MOOOOOOOOOOOOOOOOOOOOOlan.

HELLO!!!!! MULAN IS TOUGH AND AURORA SLEEPS FOR HALF THE MOVIE! THAT'S THE BIGGEST DIFFERENCE!!!!