One of the best things I've heard lately is the Robert Capa quote, "Don't shoot what it looks like, shoot what it feels like." At workshops and conferences lately I've been preaching that photographers stop worrying about technical perfection (perfect light, tack sharp focus, etc) for the sake of mood. You can absolutely have both sometimes but if it comes to the choice of one or the other, let your answer to this question be your steering wheel: If you could only have one of those in your images for the rest of your career, which would it be?