I love Christina. She knew who she was and what she wanted from episode one. She never deviated from who she was but grew as a character. She's intelligent, focused, hilarious, loyal and flawed. Basically, a well rounded character.
If she was a spoiled brat-would she have covered for Burke, operated on Derrick from gunpoint, not rat on Izzy over that Denny fiasco, stand by Owen with his PTSD or most recently stayed awake and care for everybody for four days straight after the plane crash? If that's not putting others first, I don't know what is.