Elinor and Marianne in Sense and Sensibility have some character traits in common but most of their traits are opposites. The character traits that they have in common are that they are both well educated (though not formally educated), accomplished, sincere and loving young women. There the similarities seem to stop.
Elinor is practical and dependable. Her mother relies on her to give advice and counsel during difficult transitions as is illustrated by Elinor's important role in deciding what situation to move to after their welcome at Norland Park has expired following the death of Henry Dashwood, Elinor's and Marianne's father. Elinor is also steady in her emotions and believes that prolonged violent displays of emotion do no good for individuals or situations. She believes in guiding her heart by her head, which by no means suggests that she does not feel deeply, because she does, but that there are helpful ways and unhelpful ways of demonstrating and revealing ones deeply felt emotions. Elinor is the embodiment of the sense of the title.
Marianne is more beautiful than Elinor and leans strongly toward poetry and music while Elinor, herself certainly elegantly beautiful, has talents in painting. Where Elinor is practical, Marianne is poetical. Her concern upon being required to leave Norland Park is not for finding accommodations that will fit their needs and income but for saying farewell to Norland's leaves and the wind playing through its trees. Marianne is violent in her emotions and believes that any form or degree of restrained emotion signals insincerity and shallowness of emotional feeling. She believes that heart and head are inseparable and guide a person's way by working together, without restraint of one by the other. Marianne is the embodiment of the sensibility in the title.
These traits determine the young women's behavior in the romances that drive the plot, Elinor's hidden love for inexplicably stand-offish Edward and Marianne's loudly trumpeted love for Willoughby. Elinor respects Edward's slightly strange behavior and restrains the display of her deep feelings for him, which turns out to be to her advantage as it spares her humiliation in front of Lucy, who in jealousy confides to Elinor her secret engagement to Edward, thus explaining his strange stand-offishness. Marianne dives energetically into her deep feelings for Willoughby, even to the point of making herself ridiculous and the topic of censure for ill-judged behavior like her surreptitious visit with Willoughby to Miss Smith's home.