Newt. Maybe not a standout when it comes to "interesting," but interesting enough. Just like Ripley was merely interesting enough in the first film. Luckily, Cameron saw the potential in Ripley, and made her more interesting.
Newt is intelligent and resourceful. It's implied that her mental state at the time of her discovery is one in which her brain has shut down on emotions so they don't get in the way of her doing whatever she needs to in order to survive. That's her key characteristic: she's a survivor.
I call this fertile ground. Particularly when you extrapolate what she would be like as an adult.
If I had written an Alien 3, Newt would be much like Clare Danes' character in Homeland, Carrie, with similar kinds of mental problems. (Carrie has to constantly manage her job as a CIA operative with her bipolar disorder. She has to hide her medication - lithium, Clonazepam, alcohol - and even checks herself into a hospital for voluntary ECT treatments so she can do her job).
This is what you do in a sequel; develop character not only by upping the ante in terms of plot (alien -> aliens), but also by driving it deeper into the psychology of the protagonist. IOW, create greater intensity both externally and internally.
Luckily, Cameron understood that and, likewise, took his story in both directions.