Interesting question. Lady Macbeth is definitely exhibiting traits that would be considered "masculine" in Shakespeare's time. Notably, she is attempting to influence her husband's decisions instead of supporting them. However, there is definitely a difference between being masculine and being "a man". Macbeth demonstrates a knowledge of this in 1.7, when he says, "I dare do all that may become a man;/Who dares do more is none." He is responding to his wife's insinuation that he is not man enough to take the throne by killing Duncan. He seems to understand that killing the king would not reflect true manhood. Of course, he kills the king anyway, which opens up a whole new discussion.
Both Lady Macbeth and her husband exemplify qualities of human frailty, rather than simply those confined within their respective genders. Lady Macbeth is a woman ahead of her time in her clear focus on the ultimate promotion for her husband (remembering that we are still in an age which believes in the Divine Right of Kings). She is Machiavellian in her desire for her husband, and through him herself, to be all powerful. However, the judgement of Shakespeare is that she steps beyond strength and determination into evil and immorality, and this is why she pays with her life. Similarly, Macbeth is a brave and courageous warrior, well deserved of the honours which are bestowed on him legitimately, but brought in to check when he tries to take what he is not ordained to have: the throne of Scotland.
The characterization of Lady Macbeth in the beginning of the play reveals the fundamental sexism in Shakespeare's time, one that surpasses the accepted roles of men and women in his society. Women were seen as beings whose fundamental physical nature was different from that of men in that they were programmed by nature itself to be physically weak and emotionally nurturing. Men, in contrast, were accepted as being programmed by nature itself to be strong and emotionally bent toward physical conflict and cruelty. In contemplating Duncan's murder, Lady Macbeth first seeks supernatural intervention to change her basic feminine nature so that she will be capable of the cold cruelty necessary to kill the king. She also worries that her husband lacks the natural cruelty of the male to carry it out. So, in the context of Shakespeare's audience, Lady Macbeth is "more of a man" than her husband in the beginning.
Once the king is murdered, however, he quickly makes up the difference. Macbeth goes on to commit a series of vile murders without his wife's prior knowledge, and she reverts to her own basic feminine nature. In the play's conclusion, she is weak and emotionally undone by the horror of the crimes.
I think that the previous posts do a great job of exploring the characteristics of both characters. I would caution that the phrasing of the question might seek to do what Shakespeare himself is seeking to avoid. One of the most compelling elements of Shakespearean work is the idea of how the human predicament is revealed. Whether by design or unintentional, he seeks to create a realm where individuals are not bound by gender as much as their own frailties. The mistakes and errors they possess are, to a point, universal, ones that can be held by anyone in the "perfect storm" of circumstance. Both husband and wife possess flaws that seem to work off of one another.
Whenever a reader critiques a literary work, he/she must always consider the time period in which this work has been written. For instance, in Shakespearean times, there was no woman suffrage or liberation. Often women's roles in drama are to be supportive as are Portia in "The Merchant of Venice" and Portia of "Julius Caesar" along with many others.
Now, in "Macbeth," Lady Macbeth goes beyond being supportive to taking the commanding role, one usually reserved for the male. Thus, this perversion of roles carries on the motif of the play: "Fair is foul." So, while Macbeth waivers--"If it were done when 'tis done, then 'twere well/It were done quickly"( I,vii,1-2)-- as a stereotypical woman would, his wife is decisive and assertive, traditionally male characteristics. She accuses of Macbeth of having lost his manly traits:
When you durst do it, then you were a amn;/And to be more than what you were, you would/be so much more the man.(I,i,47-51)
She accuses Macbeth of weakness and declares her "strength" and resolve by declaring that if she had decided to take action against Duncan as Macbeth has, she
would, while it was smiling in my face,/Have plucked my nipple from his boneless gumes,/And dashed the brains out, had I so sworn as you/Have done to this. (I,i,56-58)
Then, when Macbeth yet falters, asking, "If we should fail?" Lady Macbeth counters,
We fail?/But screw your courage to the sticking-place/And we'll not fail...(I,i,59-60)
Certainly, Lady Macbeth is crueler and colder than her husband; and, taking murderous action, she assumes the dominant role, and, as such, appears more manly, especially when compared to her husband whose reputation as a warrior who is never hesitant in battle. But, is she truly more manly than Macbeth? In essence, probably not. She simply embraces evil sooner than he.
Macbeth goes ahead and kills Duncan but you are right ,he understands that the killing of Duncan would not reflect true manhood. Lady Macbeth is the true force behind the murder. This poses the question as to the actual nature of their characters and whether conflict is masculinity/femininity, good /evil, poweful/powerless, beautiful/ugly........
But overall, are there any moments in which Lady Macbeth is more of a man in comparison to Macbeth?
Earlier in the play, Lady Macbeth directly insults his 'manliness' and seems stronger than her husband; does this make her a man, or just plain cruel?
May be that over-enthused by her wifely attachment to her husband, Lady Macbeth aspired to be more manly than Macbeth's self-divided manhood. She invoked the forces of darkness and disorder to 'unsex' her, to turn her 'milk' into 'gall', to 'chastise' her husband with the 'valour of my(her) tongue'. It was she who prepared the blue-print of the Duncan murder; it was she who went back to Duncan's bed-chamber to leave the dagger beside the grooms and also to smear them with the murdered king's blood. But Lady Macbeth couldn't kill Duncan for he looked like her own father; she fainted after the murder was discovered and Macbeth poetised on the ghastly sight; she regretted thereafter--'Naught's had, all spent......'; she sleep-walked and spoke her guilt in her 'slumbery agitation'; she committed suicide to escape her unbearable burden of over-doing her role, her error to become more of a man than Macbeth.