At the beginning of the balcony scene (Act II, scene ii) Juliet is professing her affection for Romeo to what she assumes is an empty orchard. She has no clue that Romeo is actually standing in the shadows beneath her. When he reveals himself he had the upperhand, as he now knows of her feelings. Juliet presses him, then, to express his own feelings. As the conversation continues both Romeo and Juliet profess their love for one another and the desire to get married. Juliet, however, is torn between the love she feels and the logic of the situation--namely, that this is all too rushed and that she is a Capulet and he a Montague. Romeo, on the other hand, (and as always) proceeds full stream ahead without any thought to the logic consequences of such emotions.
I find Juliet to be the thinker in Act II. Juliet wonders why so much emphasis in life has to be put on identity. Thus, she references what is in a name, specifically Romeo Montague's.
Juliet fears for his safety as her kinsmen would kill him if they found him there. Later, she doesn't want him to think she is "too quickly won." This shows she has concern about her reputation with Romeo. She references how fast she is falling for him, but that's not really like her.
Romeo on the other hand is completely impulsive. He has no fear of being there, he loves her deeply already and is ready to swear a vow to her tonight.
Juliet is a little apprehensive, thus she notes this situation is "too rash, too sudden, too ill-advised." Romeo tries to talk her out of that perspective and succeeds committing to meet one she would send to him tomorrow to learn of the plan after he meets with a friar.
Under normal circumstances, Juliet strikes me as one who wants to think through things, whereas Romeo just does what he feels in the moment.