Donna Noble (Doctor Who)
Rory and Amy tie for second
She's definitely among my top 10 favorite fictional characters, or at least in the top 100. Originally a loud-mouth, obnoxious woman, her feistiness hid deep insecurities about herself. What seems to be a self-absorbed woman turned out to be possibly the most caring companion of the new series.
She was actually pretty innovative - her sneaky behavior in the first episode of series four proved how proactive she could be, and how her run-in with the Doctor just made every normal day feel so boring. Coupled with her mother's put-downs and general lack of faith in her, and the fact that her fiance turned out to be drugging her, she was not a happy camper. Still, she looked out for her grandfather and loved his weird behavior.
I really was expecting her to be a shallow twit when I first saw her. The Fires of Pompeii
is one of my favorite episodes of the series, and my favorite episode of the Russel T. Davies era. (My second-favorite would be the episode where Rose was trapped in another world and broke down crying. Which reminds me, should I make a blog ranking the DW companions?) It was sort of a shitty episode, but Donna was just amazing in this episode. She wants to save people from the inevitable eruption that would doom everyone in the town, despite that not being possible because fixed points and time paradoxes and all that shit. She ends up having to make the volcano erupt, dooming the town in order to save the rest of the world from the aliens. The Doctor could have pulled the lever and killed all those people by himself, but Donna chose to share the burden with him. (Which makes me look at the 50th anniversary special in a different light.)
And after all that, she still tries to save people. Even though she has no chance of doing so, she runs around screaming in a vain attempt to save anyone she can. It's her breakdown in the TARDIS
that convinces the Doctor to go back and save the family they've been working with throughout the episode. (Why didn't the Doctor save the people who were right there? a) The Doctor gets really jaded at times, particularly during series 7's first half, b) because he's probably upset about how he doomed his home and loved ones just like this earlier, or c) because the script said so.)
I really like her for the same reasons I like a lot of people on this list: because she has a big heart despite appearing to be a shallow, weak or naive. And even beyond her sweetness, she's a smart, funny, and courageous woman who really built on the problems and strengths of the past two Companions and fixed them.