Act 1 begins with the witches talking about meeting up with Macbeth. They don't seem like good witches. Then in Scene 2, readers and viewers hear good reports of Macbeth's bravery in his defense of king and country. So my very first impression of Macbeth is somewhat confused, somewhat questionable.
But my first impression of Lady Macbeth isn't confused at all. Scene 5 begins with her reading the letter from her husband about his promotion and the witches' predictions. She has an assertive, pushing, strong character that creates a negative impression with its total disregard for human life other than her own.