Ethical theories are limited. A working combination of several seems best. If I were a politician, I'd act mostly as a Utilitarian for the public good; but in my personal life, I prefer Aristotle's Virtue Ethics. In Sartre's brief critique of Kant in Existentialism is Humanism he shows how deontology cannot give advice on how to act in a particular situation when duties conflict. Deontological duties need to be fine tuned in the sense that the respective duties have to be valued in relation to one another. Lying to save a life, for example, shows that saving a life is a more valuable duty than the duty to always tell the truth.
