I like characters that are ambivalent. It keeps options with them wide open and they make for interesting reading. Willl they do the right thing by the hero/heroine? Willl they betray them to their enemies? I am impressed with the character of Missy on Doctor Who right now for this reason. You know she's bad but there's enough hints there is more than that to her and so you want to see how things pan out and what effect that will have on the Doctor.
I use traits to drive motivation as well. A well motivated character acts consistently, will go beyond their limits to achieve their objectives and will achieve far more than they would otherwise have done. That's true for us too!