Emma is filled with important quotes, and various readers will pick and rank various quotes differently; however, I think a safe bet is to pick quotes that highlight particular themes in the book or are especially good at showing the characterization of a specific character.
Love and marriage are two themes that run strongly throughout the text, so I would pick quotes that apply to either of those two themes. Chapter 31 offers two solid quotes about love and Emma's attitude about it by that point in the story. The first quote is from paragraph two, and the second quote is from paragraph four.
I certainly will not persuade myself to feel more than I do. I am quite enough in love. I should be sorry to be more.
. . . they say every body is in love once in their lives, and I shall have been let off easily.
The next quote comes from chapter 48, and it is an especially good quote because it shows readers that Emma has finally come to realize exactly how much Mr. Knightley means to her.
Till now that she was threatened with its loss, Emma had never known how much of her happiness depended on being first with Mr. Knightley, first in interest and affection.
A great deal of what makes Emma so great is how she feels about love and marriage. The following quote is quite harsh, but it does illustrate her character quite nicely.
Oh! to be sure [. . .] it is always incomprehensible to a man that a woman should ever refuse an offer of marriage. A man always imagines a woman to be ready for any body who asks her.