One significant difference between Romeo and Juliet in the famous balcony scene, Act II, Scene 2, is that Romeo is depicted as being romantic and fanciful, while Juliet is portrayed as being far more logical and reasonable.
Romeo's opening two speeches are full of metaphors, similes, and personifications that show his romantic nature and show how he is romanticizing Juliet and the issue of their relationship.
An example of a metaphor is, "It is the East, and Juliet is the sun!" This metaphor serves to liken Juliet to the sun, portraying her beauty as radiant, which idealizes Juliet. A simile that also serves to idealize Juliet in the same way is found the second speech:
For thou art
as glorious to this night, being o'er my head,
As is a winged messenger of heaven. (2.2.28)
This simile, comparing Juliet to an angel, serves to idealize Juliet by making her appear to be above him in beauty and morals. An example of personification that serves to idealize Juliet by capturing the beauty of her eyes is seen in line 15:
Two of the fairest stars in all the heaven,
having some business, do entreat her eyes
To twinkle in their spheres till they return.
Romeo personifies the stars as communicating with Juliet's eyes, making them twinkle like stars, thereby also comparing her eyes to stars.
In contrast to Romeo, it is clear that Juliet, in her opening speeches, is not romanticizing and idealizing Romeo, but rather deeply analyzing the issue presented by her love for him. We particularly see this in the use of Juliet's language. Instead of using flowery metaphors and similes, she uses rhetorical devices to formulate her thoughts.
Epanalepsis, which is a form of rhetorical redundancy, is seen in line 35. Epanalepsis is created by taking a word at the beginning of a clause and repeating it at the end of the clause. Juliet's line, "O Romeo, Romeo! Wherefore art thou Romeo?," repeats "Romeo" at both the beginning and end of the sentence. The line serves to show that instead of idealizing Romeo, she is carefully reflecting on the problem of his family name and analyzing whether or not it should be considered a problem.
A second rhetorical device Juliet uses is Polysyndeton, which makes use of many conjunctions. The repetition can make one feel dizzy and overwhelmed. In line 42, we see polysyndeton with the repetition of the conjunction "nor" in Juliet's argument:
What's Montague? it is norhand, nor foot,
Nor arm, nor face, nor any other part
Belonging to a man.
Juliet is repeating the conjunction "nor" to analyze all the things that a Montague is not, thereby creating an overwhelming effect and argument that the name is insignificant, showing us just how carefully she is analyzing her current problem.
Hence the major difference between Romeo and Juliet in the balcony scene is that Romeo romanticizes and idealizes Juliet with flowery language, while Juliet analyzes the problem their relationship poses, using careful, rhetorical language.