The relationships between the couples Hero and Claudio and Beatrice and Benedick are so different because Shakespeare is showing us two opposite poles of love. Hero's and Claudio's relationship represents a surface level physical attraction, while Beatrice's and Benedick's relationship has lasted a great deal longer and involves an attraction of minds.
We have evidence that both couples' relationships actually began before the wars Don Pedro and his company have just returned from. However, Claudio indicates that his attraction for Hero is based on looks while we know that Beatrice and Benedick frequently engage in battles of the wits, showing us that their attraction is based on each other's brains and humor. After meeting Hero, Claudio confesses to Benedick that he thinks Hero is the "sweetest lady that ever [he] looked on" (I.i.160). Later, in this scene he tells Don Pedro that before the war started he looked at Hero with a "soldier's eye" and liked her, but his task of war drove the thought of love from his mind. Now that the war is over he sees "how fair young Hero is" and knows that he "liked her" even before the wars started (225-263). At this point, as far as we know, Claudio and Hero have never really had a conversation together, nor do they say anything to each other until their betrothal has been arranged through Don Pedro. Hence, we can fully see that Claudio's attraction for Hero, as well as possibly Hero's attraction for Claudio, is based purely on physical looks.
In contrast, we learn in the first scene that Beatrice and Benedick certainly have conversed together prior to Benedick's return from the wars. In fact, we learn from Leonato that, "There is a kind of merry war betwixt Signior Benedick and [Beatrice]. They never meet but there's a skirmish of wit between them" (50-53). Not only that, there are also certain clues that Beatrice had feelings for Benedick at one point, but that he sabotaged them somehow. The best clue can be found at the masquerade ball. After Beatrice insults Benedick, Don Pedro tells Beatrice that she has "lost the heart of Signior Benedick," meaning that she has put him down (II.i.243-244). Beatrice responds by replying that he had indeed lent her his heart once and that she "gave him use for it--a double heart for his single one," meaning that she repaid him with her own heart (245-246). She also claims that Benedick stole her heart from her dishonestly, as we see in the line, "Marry, once before he won it of me with false dice" (246-247). We don't exactly know what she is referring to, but we can see it as proof that Beatrice had feelings for Benedick but that he somehow sabotaged those feelings. Since we know that Beatrice earlier had feelings for Benedick and since they constantly engage in battles of wits, we can say that their feelings for each other are based more on their inner qualities, such as their personalities and minds.
Hence, we see that Shakespeare created such drastically different relationships for the couples Claudio, Hero, Beatrice and Benedick in order to show the two opposing sides of love, physical attraction and deeper attraction.