Both Macbeth and Banquo are bewildered by the weird sisters. The witches proclaim that Macbeth is Thane of Glamis and Cawdor, and will eventually be king. Banquo asks Macbeth why this news startles him. Banquo asks the witches to tell his future. They say that he will not be king, but his sons will. Given Macbeth's first reaction, it seems that Banquo is initially more comfortable with the prophecies than Macbeth is.

Seeing proof of what the witches had said, Macbeth becomes ambitious. Banquo, on the other hand, collects his thoughts and becomes skeptical. Here, we clearly see how Macbeth gives in to his ambition while Banquo takes a step back and employs a healthy (intelligent) skepticism:

And oftentimes, to win us our harm,

The instruments of darkness tell us truths,

Win us with honest trifles, to betray's

In deepest consequence. (I.iii.133-46)

After hearing Banquo's warning, and considering how "foul and fair" the day has been, Macbeth is skeptical as well. So, both men share a healthy skepticism. But Banquo inevitably accepts the notion that if the future matches the witches' prophecies, so be it. Macbeth becomes more obsessed with the prophecies and his future. Macbeth's ambition and his wife's influence will feed this obsession.

In this particular scene, Macbeth is skeptical but intrigued to the point of being obsessed. Banquo is skeptical and careful in thinking about the encounter.