I'd have to say my least favorite is probably Sansa Stark. I can't stand the stereotypical helpless female archetype. Most of the other female characters are able to maneuver in their circles well, even if a lot of them are stuck doing streotypical female roles.
Sansa seems fairly worthless in every way other than being the heir apparent to Winterfell (since Robb is in open rebellion and will be killed as a traitor if he's caught and the younger Stark boys are thought to have been killed at the hands of Theon Greyjoy) and by association the entire North.
I just can't stand her lol. Cersei may be evil, but she isn't helpless. Catlyn may be ditzy, but she stands up for what she believes in. Dany has the constitution of a queen through and through. Arya is a little badass.
Sansa is freaking WORTHLESS. OMG I hate her lol. Freakin' victim mentality in her.
No, really, tell us how you really feel Rob....

I agree that although she is helpless, she is just trying to play the part of a future princess the only way she knows how... Afterall, she is separated from her mom, her dad is dead, and the only examples that she has are the Lannisters and the Tyrells.
And even though she is only 17 in real life, I personally think that she is gorgeous. Once again , the whole redhead thing....