her sister's suitor CharlesBingley as a simple and good-hearted young man.

Truly, Elizabeth is a keen observer of people. She thinks she has everyone figured out. Due to her pride, Darcy is the last man on earth with whom she could be. Cleary, Elizabeth is prideful and prejudiced. She refuses to accept the fact that Darcy could be worthy of her love.

Jane is adorable in her sweet, trusting nature. Jane is content in pleasing others. Even Jane's father assesses her as too willing to please others:

Her father considers her too willing to please and believes that she lacks the character to deal with life's difficulties. He tells Jane, "You are . . . so complying, that nothing will ever be resolved on; so easy, that every servant will cheat you; and so generous, that you will always exceed your income."

Both sisters are lovable in their own unique ways. Eventually, each sister finds the happiness in which both are so deserving.

Jane Austen's novels often feature contrasting characters, as a literary foil to highlight or showcase particular qualities of another character.  Pride and Prejudice has several good examples of literary foils:

Mr. Darcy vs. Mr. Collins

Both are potential suitors to Elizabeth's hand, and both make the mistake of a terrible marriage proposal; Austen uses the odious Mr. Collins show the reality of what many women like Charlotte Lucas had to consider: a loveless marriage in exchange for security and comfort.  When held up next to each other, Mr. Darcy's positive attributes outshine Mr. Collins; both were possible choices for Elizabeth to marry, but in the end, she shows wisdom in waiting for a man she could truly respect and love.

Lydia Bennett and Elizabeth Bennett

Lydia makes Elizabeth look good in the story; to be honest, Lydia could be the poster child for bad decisions and behavior in Regency England.  She has none of Elizabeth's finer qualities, and her outrageous behavior sharply contrasts Elizabeth's good sense.  Lydia is without a doubt, one of the "silliest girls in England" as her father described her, but it is really her decision to elope with Wickham that Austen uses to drive home a hard point about marriage and family.  Lydia's selfish decision to elope brings shame to the family, but Elizabeth's outstanding marriage to Darcy honors the family.

In addition to not being wealthy or of very high social status, Elizabeth Bennet is intelligent and frank. She is respectful to others, including her very silly mother, without being fake or pretentious. Elizabeth wants happiness for her older sister and doesn't presume to judge her choices. She is attracted to Mr. Darcy but is too proud to play games to get him. She won't tolerate his insults to his family or to her. She is forthright about things.

Caroline Bingley, by contrast, is forthright about nothing. She is all about playing social games, whether concerning her own romance or her brother's. Status in society is everything to her, and she is willing to do what is necessary to preserve or increase it. She tries to prevent her brother from marrying Jane even as she pretends to like her and enjoy her company. Caroline judges both Jane and Elizabeth on the superficial standards of wealth and family status. She wants Mr. Darcy, too, but won't express herself directly to him, preferring to try to manipulate him.

The characters of Caroline Bingley and Elizabeth Bennet in the novella Pride and Prejudice are hard to compare and easier to contrast.

Caroline Bingley is unmarried and rich, but does not have any aristocratic background. For this reason, she is very subservient to Mr. Darcy and basically woos him to get his attention. She seems to be unsure of herself, which is manifested in the way that she tries not to speak her mind too much, and is agreeable to everything that Darcy says and does. Her ultimate goal is to become the future Mr. Darcy. She clearly sees that Elizabeth is her competition and, for this reason, she talks about her negatively.

Elizabeth was also unmarried. She was not rich, nor did she have a dowry  substantial enough to propose herself as a potential wife to a man as rich as Darcy. She was not an aristocrat either. Yet, in contrast to Caroline, Elizabeth did not care at all about rank, position, nor money. All she wanted was to truly love someone. She was an independent thinker, spoke her mind, and did not make distinctions when it was time to say what needed to be said.

If the two women were to be compared, the only things that they had in common were that they were both of a "marriageable" age, that they were not aristocrats, and that they got along well with Jane (until Caroline betrayed her). Other than that, the women contrast almost completely.

Elizabeth is much more prone to show her emotions and to jump to quick judgments than Jane. Elizabeth easily becomes prejudiced against people, as the title of the novel indicates. The chief person who earns her wrath is Mr. Darcy, who insults her when she overhears him saying she isn't pretty enough to dance with. This leaves her open to believing without question Wickham's false tales of being wronged by Darcy.

Jane is more cool and cautious, both about showing her emotions and about judging people. This can be both good and bad. As Charlotte Lucas warns, if Jane doesn't show more warmth and affection for Bingley, he is likely not to understand how interested she is in him. Darcy certainly underestimates the strength of Jane's feeling when he advises Bingley not to get any more entangled with her.

In Elizabeth's case, showing her passions is both good and bad: her high spirits and open disrespect for him cause Darcy to fall in love with her, but when he proposes marriage to her the first time, her fury gets the better of her, and he ends up with a tongue lashing she later regrets when she finds out the Wickham lied about him. Likewise, Jane's coolness and reserve keeps her from making snap judgments or losing her temper, but also leads Bingley to thinking she is not truly in love with him. 

The two complement each other because Elizabeth urges Jane to more passion and Jane urges Elizabeth to more caution. They are very close to each other and, despite their flaws, more intelligent than the other females in the family. 

It is certain that Caroline Bingley and Elizabeth Bennet are used as foils in this novel. Both, after all, find themselves competing for the affections of Mr. Darcy. It is clear that Caroline Bingley feels threatened by Elizabeth Bennet and that she uses every means at her disposal to try and attack her character and standing with Darcy. Note how the author introduces Caroline Bingley and her sister in Chapter Four of the novel:

They were in fact very find ladies; not deficient in good humour when they were pleased, nor in the power of being agreeable where they chose it; but proud and conceited. They were rather handsome, had been educated in one of the first private seminaries in town, had a fortune of twenty thousand pounds, were in the habit of spending more than they ought, and of associating with people of rank; and were therefore in every respect entitled to think well of themselves, and meanly of others.

At every stage in the novel, when Elizabeth and Caroline are together, it is clear that this level of pride comes through in what Caroline Bingley says, and how she behaves. For an example, consider her behaviour towards Elizabeth when she stays at Netherfield with them during Jane's illness. Caroline Bingley is another character who is an example of pride and its faults. The main differences between Caroline Bingley and Elizabeth are therefore the social standing of Caroline Bingley and her pride, which causes her to act in ways that Elizabeth finds superficial and hypocritical.