Sense and Sensibility was the first of Jane Austen's six major works to be published and it was originally an epistolary novel, written when she was about nineteen. The legacy of the letter format shows in the long speeches made by some characters, particularly Elinor, where she takes on a didactic tone. It could be argued that it is Jane Austen's only novel of ideas, where she reveals awareness of the growing ethos of Romanticism and fears its influence - whilst being drawn under its spell.
It is accepted that Elinor represents sense or what we would call common sense, although she is not devoid of emotion. Marianne is the vehicle of sensibility - in modern terms sensitivity - although she can use her reason. They are not stereotypes.
Perhaps the feeling of the novel is best expressed in Persuasion, Chapter 11: "... she ventured to recommend a larger allowance of prose in his daily study." Poetry and emotion are all very well but the rationality and mundane nature of prose is to be respected. The paradox is that Marianne is - to many readers - a more appealing character than Elinor and one whose eventual marrying off to the flannel-waistcoated Colonel Brandon is a disappointment.
Whilst Jane Austen never treats Elinor with irony and appreciates the need for decorum, sense and propriety in life, the actual writing also sympathises with her wilful sister, despite her dangerous and impulsive actions. It isn't as simple as head versus heart: we, as readers, receive the impression that the author is torn between two attitudes to life at the cusp of ideological change.
I am not arguing that there is no element of thoughtfulness in the other novels. Yet, Sense and Sensibility is governed by abstract ideas prevalent at the time: the theme is more obvious and embodied explicitly in the central characters. Although Jane Austen mocks Marianne's "transporting sensation" over the dead leaves that Elinor views in matter-of-fact fashion, she has created an endearing portrait. Which sister do we remember years after we have read the book?