The re-read threads for both Tyrion and Arya have pointed out many narrative tricks that Martin has used to cast the characters in a sympathetic light, starting with their introductions early in GOT. Arya is a modern character and is therefore easy for us to identify with. Her values and attitudes are similar to our own. I've often heard Tyrion described as the author's avatar and it's well known that he is Martin's favorite character.
In contrast, Catelyn and Sansa are portrayed negatively, with that approach seeming the strongest in GOT as well. Both characters are very much products of their world. Sansa has been raised as the eldest daughter of one of the most powerful Houses in Westeros and was being groomed for her future role of Lady Wife. She is portrayed as class-conscious and overly naive, sometimes to the point where it strains credulity. Her actions serve to set her apart from the rest of her family, at times leading to a permanent dispike by some fans. Catelyn is also very much a product of her world. She is a woman who thinks of her family's political needs and carries the negative beliefs regarding bastards. From the beginning, she is cast in oppositon to Jon, a character who is presented as "good" almost from the opening lines of the books. These two characters almost appear alien to us, especially when compared to Arya and Tyrion.
Despite the different approaches taken to these four characters, they are still considered some of the best written and most complex characters in the series. Their story arcs engage us and their characters grow through some dramatic changes, whether that is Sansa's loss of innocence, Cat's journey into ever deepening grief, Tyrion's struggle over whether to embrace his inner monster, or Arya's growing rage and thoughts of vengeance.
Martin appears to be playing with reader expectations, breaking from traditional expectations of characters. By doing so, Tyrion's story at the end of Storm and further in to Dance appears more shocking to us readers. For characters such as Sansa and Theon, they seem to be almost different people than where they started the series. The POV structure GRRM uses forces us to constantly reevaluate our understanding of the story and the characters.
Yet, comments from GRRM may point to another reason behind his decisions:
(Chicago, IL; May 6-8)
At the koffeklatche, George said the two favorite characters were Tyrion and Arya. The least favorites were Sansa and Catelyn. (This annoyed me to no end, as Sansa is my personal favorite.)
[Note: The precise date, beyond July 2000, is unknown.]
(3) Arya was one of the first characters created. Sansa came about as a total opposite b/c too many of the Stark family members were getting along and familes aren't like that. Thus, Sansa was created; he ended by saying they have deep issues to work out.
Amazon.co.uk: You write children well.
The hardest chapters for me to write are the ones about Bran, just because he is the character most involved in magic, the youngest child and he is so seriously crippled--I have to write in that sense of powerlessness and it has always to convince. Sansa was the least sympathetic of the Starks in the first book; she has become more sympathetic, partly because she comes to accept responsibility for her part in her father's death. Jon Snow is the truest character--I like his sense of realism and the way he copes with his bastardy.
Martin's least favorite characters happen to be Sansa and Catelyn, the same two who he has written in a less sympathetic manner. Is it possible that Martin chose to write his favorites in a more lenient manner, perhaps even unconsciously?
So, in a series filled with complex and rich characters, what has led Martin to choose which characters to portray in a sympathetic manner? Perhaps even more importantly, what did he hope to accomplish? And perhaps most important of all, knowing that Martin does this, what does this mean for us as readers and should it lead us to reconsider our opinions regarding some of the characters?