One way we see Shakespeare contrast Beatrice with Benedick is that Beatrice is more emotionally driven while Benedick remains more logically minded. This contrast helps to illuminate Shakespeare's theme of the differences between men and women.
One way in which we see Beatrice be more emotionally driven than Benedick is that her spoken reaction to being tricked into believing that Benedick is in love with her is much shorter than Benedick's own response. Even though both characters proclaim that they must amend their ways and give up their pride, Beatrice's short response is full of emotion, even exclamation points, such as "Contempt, farewell!" (III.i.111). In contrast, Benedick's much longer speech shows us that he must spend more time reasoning his way into his new situation. Beatrice becomes convinced that she should requite Benedick's love simply by hearing Hero and Ursula praise Benedick, showing us that, despite her protests, Beatrice already thought highly of Benedick. Beatrice's quick acceptance of Benedick in her short little speech show us that she is very emotionally responsive. We especially see Beatrice's emotional responsiveness when she proclaims that she should love Benedick because others think he deserves it, as we see in the lines, "For others say thou dost deserve, and I / Believe it better than reportingly" (III.i.117-118).
In contrast, Benedick takes a much longer time to reason through Beatrice's attributes. He must examine every merit both Claudio and Don Pedro said Beatrice has, as we see in his lines:
They say the lady is fair--'tis a truth, I can bear them witness; and virtuous--'tis so, I cannot reprove it; and wise, but for loving me ... " (II.iii.210-212).
The line, "'tis a truth, I can bear them witness," particularly shows us that he is not only reasoning through to see if he agrees with their description of Beatrice, he is also examining whether or not he will be embarrassed by his own decision. We further see him reason through his emotions when he points out that he may be laughed at for changing his mind about love and marriage, but says it will be okay because everyone changes their minds with age, as we see in the lines:
I may chance have some odd quirks and remnants of wit broken on me because I have railed so long against marriage. But doth not the appetite alter? (II.iii.214-216)
All of the reasoning we see through this very long speech, in contrast to Beatrice's very short speech, shows us that Benedick is more inclined to use rational thought while Beatrice is more emotionally driven.