Fighter of the Destiny (择天记) has two of the best gray people. They are not the firmly-on-the-dark-side, bad guys. They are, however, good people who make bad choices.
I think the best drama villain is the one who does terrible things for the right reason. Sheng Hou massacred an entire academic branch, executed most of her husband’s family, ritually slaughtered thousands of prisoners, not to mention she sacrificed her only child in order to preserve the stability of the kingdom. In her mind, a ruler has to get her hands dirty to do what’s best for her people. The blood on her hands is a testimony to her resolve. This woman has never lied to herself. So it is especially satisfying to see her redemption after she has (almost) descended into madness.
Her exact opposite is Qiu Shan Jun. He is a good person who is always trying to do good. The one time that he act selfish and petty, he got suckered into the bad guy camp. Because he couldn’t reconcile what he wanted to be and what he actually was doing, so he lied to others, and worse of all, he lied to himself. His lies quickly snowballed into an avalanche that buried his conscience.