I would choose the phrase that precedes the "partnership" descriptor. Macbeth says that he wrote of the witches prediction because "This have I thought good to deliver thee."
This small phrase is very illuminating. He is deferring to his wife. He "thinks" he should make her informed of this news and that she'll be happy. He doesn't say: look, I have good news. He doesn't say "this is what we are going to do". He says he thought it "good to deliver thee". Macbeth is subservient in all aspects - to Duncan, to the witches, and to his wife. This describes their marriage because, as later scenes will show, he does what she asks of him. Hence all the trouble!
In his letter to Lady Macbeth, Macbeth tells her that he has been awarded the title of Thane of Cawdor; furthermore, he shares the news of his encounter with the witches who have made exciting prophecies. He addresses his wife as "my dearest partner of greatness," indicating that this marriage is indeed a partnership; decisions are made together. Despite this description, however, when Macbeth returns to Inverness, it is clear that the relationship between this husband and wife is not based on equality. She plays a powerful role in convincing a reluctant Macbeth to kill Duncan that night. Later Macbeth will make a number of crucial decisions without consulting Lady Macbeth at all. Their marriage is deeply affected by the witches' prophecies and their subsequent rise to power.