What is this biggest betrayal in Macbeth?

This is an interesting question and up for speculation. I always felt that Macbeth's betrayal of Banquo was the most significant. Banquo was Macbeth's right hand man and friend. They had been through wars together and both had experienced the weird sisters at the same time. Macbeth's relationship was problematic from the beginning because L. Macbeth was already manipulative towards her husband before the witches showed up. Macbeth's relationship with Banquo was much clearer and based on honour. I find Macbeth's betrayal of Banquo, including the attempted murder of his son, most disturbing.