By far, Macbeth's death is more tragic than that of his wife. The tragedy of Macbeth's death stems from the fact that he had the POTENTIAL for greatness; he was a successful, respected general who turned away from his true destiny and created/succumbed to an alternate reality that brought nothing but pain and even death to himself and those close to him. In short, he had life in the palm of his hand and ruined everything. Compare that with Lady Macbeth's character: she appears as a yes-man to evil and shrivels almost immediately after the initial deed is done.
If we understand the tragic hero in the traditional Aristotelian sense, I would argue that Lady Macbeth is a good deal less tragic than her husband. We do not see her as a complicated individual who is good, better than most, great in fact, but with a flaw that results from her greatness. We see her as flawed and evil from the first moment we meet her. Macbeth, however, is great: he is a courageous warrior, and those virtues which make him that are what bring him down: his violence in particular. That, and his ambition (which also makes him a great warrior), and other things--such as the temptation of the witches and being seduced by his wife. From the first moment we meet Lady Macbeth she seems evil--we have no exposition that she might have been a good person before the events of the play. We can not measure her "fall" as tragic unless she begins at a "height," and I do not think she does.
Well, I think this is an more of an opinion. Personally, I feel Lady Macbeth might be a bit more tragic due to her husband's uncaring attitude of her plight at the end of the play.
They conspired together, and both suffered the effects of guilt through sleep disorders, and madness. Their drive for power led them to this point, together, yet in the end, it seems more tragic that she went to her death alone.