I like Elizabeth most (and Darcy second!). Austen meant for us to focus on Elizabeth and draws Elizabeth with a very "fine paintbrush" on a very smooth "bit of ivory," thus making her stand out, good points and bad points, in clear relief. We know Elizabeth and, knowing her, like her. She is the center, the axis, around which everything else revolves and to which everything else compares and relates. In short, I like Elizabeth most because Austen did a wonderfully good job in creating her!
Because editors are only allowed to answer one question per posting, I edited yours down to just the first question you asked.
If by 'role' you mean 'character', then in order to answer the question you need to ask yourself who did you care about the most? Whose plot line were you most interested in? Who did you agree with? I can't answer the question for you, but I can give you a few key points about some of the main characters. From there, you can think about your response to these facts and make a case for your favorite character.
Elizabeth: The novel is really Elizabeth's story, so she would be the most obvious contender for 'favorite character.' Her most notable qualities are her strong will, determination, loyalty, and wanting to marry for love.
Jane: She is best characterized as pretty, pleasant, optimistic, a bit naive, and also wanting to marry for love.
Charlotte: She is best characterized as pleasant and practical. She is less interested in emotions and more interested in the practical aspects of marriage, especially financial security.
Lydia: She is silly and flirtatious, which leads her to be foolish and self-centered. She is a frankly a bit hard to like.
Mrs. Bennet: She is intensely interested in getting her daughters married and married well. She has their, and her, best interests at heart, but can be abrasive and a bit foolish.
Mrs. Gardener: She is a wonderful influence and confidant for Elizabeth. She is practical, but also has a romantic heart and understands Elizabeth.
Darcy: He doesn't make a great first impression, but as we get to know him through the novel, he becomes the romantic hero who saves the Bennet family reputation and proves to Elizabeth that he is man worthy of her high standards.
Bingley: He is a kind, gentle man who loves Jane, but is easily influenced by his friends and family. He makes things right with Jane in the end.
Lady Catherine: She is a haughty and arrogant Lady who doesn't miss a chance to impose her will or opinions on those "beneath" her.
Mr. Collins: He is a fawning man who blunders into a proposal to Elizabeth, but ultimately ends up married to Charolotte. He talks too much and doesn't seem to have many social graces.
Personally, I like all of the characters for what the contribute to the WHOLE of the novel. Even the characters that aren't that likeable are kind of fun to be annoyed by! You will need to decide what your focus is going to be in response to the question. Are you looking for a character you admire? Or are you looking for a character you enjoyed reading about?