In contrast to Macbeth, who is almost immediately enthralled by the witches' prophecies that he will be made Thane of Cawdor and "shalt be King hereafter" (1.3.51–53), Banquo is skeptical of the witches "That look not like the inhabitants o’ the earth," and he's even more skeptical of their prophecies.
Banquo no doubt shares Macbeth's doubts about the prophecies that "The Thane of Cawdor lives" (1.3.75), and "to be King / Stands not within the prospect of belief," (1.3.76–77), but Macbeth accepts his prophesied fate, and he's already thinking about how he can make the prophecies come true as soon as possible.
Rather than simply accepting the prophecies as truth, Banquo wants to test the witches further.
BANQUO. If you can look into the seeds of time,
And say which grain will grow and which will not,
Speak then to me (1.3.61–63)
The prophecies that the witches make to Banquo are notably less specific and straightforward—and considerably more ambiguous—than those they made to Macbeth.
FIRST WITCH. Lesser than Macbeth, and greater.
SECOND WITCH. Not so happy, yet much happier.
THIRD WITCH. Thou shalt get kings, though thou be none (1.4.68–70).
Banquo is right to be skeptical. The first two of these pronouncements aren't even prophecies, and the third ultimately proves to be false—except in the mind of Shakespeare's patron, King James I, who believed that he was descended from Banquo—because the crown passes to Duncan's descendants, starting with his son, Malcolm, not to Banquo's descendants.
Banquo suggests that he and Macbeth have "eaten on the insane root / That takes the reason prisoner" (1.3.87–88). Even when Ross tells Macbeth that Duncan has made him Thane of Cawdor, Banquo is taken aback—"What, can the devil speak true?" (1.3.113)—but Banquo is still not convinced that the witches aren't evil, as shown by his use of the word "devil," meaning the devil speaking through the witches, not the word "devils," meaning the witches themselves.
Banquo continues to have doubts.
BANQUO. But ’tis strange;
And oftentimes, to win us to our harm,
The instruments of darkness tell us truths,
Win us with honest trifles, to betray's
In deepest consequence (1.3.132–136)
When Macbeth patronizes Banquo about the prophecies—Macbeth is already thinking about killing Duncan—Banquo is nonetheless amenable to talking with Macbeth about them, although the conversation that Macbeth suggests never happens.
MACBETH. Think upon what hath chanced, and at more time,
The interim having weigh'd it, let us speak
Our free hearts each to other.
BANQUO. Very gladly (1.3.168–171).
Macbeth makes a similar request in act 2, scene 1, in which Macbeth seems to solicit Banquo's help in usurping Duncan's throne, but that conversation never happens, either.
In all of this, however, and through the rest of the play, Banquo says nothing against Macbeth with regard to the prophecies, and until Banquo begins to suspect that Macbeth is responsible for Duncan's murder, he has nothing but good things to say about Macbeth himself.
In the next scene, act 1, scene 4, while Macbeth is thinking aloud about how he must "o'erleap" Malcolm on his way to the throne (1.4.56), and he's telling the stars, "hide your fires; / Let not light see my black and deep desires" (1.4.57–58), Banquo is praising Macbeth to Duncan.
DUNCAN. True, worthy Banquo! He is full so valiant
It is a peerless kinsman (1.4.61, 65).
Macbeth is a "peerless kinsman," indeed, who murders Duncan and takes his throne.