Sansa - The book does a better job of giving some background as to why she is how she is, but basically she has the grace and good looks of her mother, she's good at "girly" things like needlework, and she has these typical girl fantasies about marrying a prince, being a princess, having lots of kids, and being a queen, living in a castle, etc. It's not that she's a bad person, she's just like so many young girls are, full of ridiculous dreams that they want so bad they can taste it, except she's being given an opportunity to fulfill those dreams, and she's starting to find out, as others are finding out, that idealism, and naivete are terrible flaws. Where we are in the series with Sansa is the crumbling of her fairy-tale dreamlike expectations of how the world is supposed to be, and in its place, we see a ruthless, backstabbing, power-centric world where "When you play the game of thrones, you either win or you die." All that to say, it's hard for me to think her too bad of a person at this point in the story because so many girls are like her at that age, and it's as if the author just plucked on up and put them in this situation, and now their idealism is confronted by reality.
Arya - The opposite of Sansa, somewhat of a cynical girl where we are. She rejects the idealism of sansa's world, but that's partly due to the fact that she looks more like her dad, doesn't enjoy the girly things, and naturally she would move more towards tomboyish activities since she doesn't fit in in lady-land. Along with that, she doesn't dream of all the things typical ideological girls dream of, like sansa, but rather she wants to be a fighter, a knight...but she can't because she's a woman. But she doesn't let that get her down, showing determinism, and strong-will (stubborn), she wins her dad over to let her practice swordfighting. She's the practical one, the one more grounded in reality because she's met opposition early in her life (not being good at the stuff girls are supposed to be good at, and not being as pretty as her older sister). So she's easier to like, but she too is a product of her environment and her physical makeup.
Jamie - At this point in the series, he seems cold-hearted but charming, which is fair enough but the book at this point made him a bit more heartless I think, or maybe that's just how I was reading him.
Tyrian - Just starting to get some new depth for his character with this latest episode. Really starting to see how he's treated by his father, some of the history with his family, etc. Really well done character in both the book and now the show.