To begin with, Lady Macbeth might appear more morally corrupt and even more fiercely ambitious than her husband. She talks up her ambition in the most blood-curdling way and eggs her husband on to murder. He, on the other hand, does appear to have some initial scruples, at least. Once he achieves his ambition, however, he is seen to go even further, not hesitating to eliminate anyone else who stands in his way. At this stage it could be said that he becomes the worse of the two.
However, if we consider the play as a whole, we do see that ultimately neither of them are able to cope with the consequences of their actions. Lady Macbeth becomes unhinged, starts sleepwalking, trying to wash the blood off her hands. Macbeth grows ever more reckless, killing more and more, but also growing more desperate and placing less and less value on life in general. He appears to reach a point of absolute psychological despair and exhaustion, before rallying himself briefly for the final battle against Macduff. He commits terrible crimes, aided by his wife but they both suffer mental anguish as a result, which would not be the case if they had been wholly corrupt. They are deeply flawed characters, but not entirely evil.
In the end, it might be said that Lord and Lady Macbeth are as bad as each other, but at the same time, they also suffer equally and in the extent of their mental suffering and essential remorse, they are also to be pitied.