Utilitarianism/ Communitarianism

After reading about these two philosophies/theories I am unsure which approach serves the most good. I understand that Utilitarianism is "the greatest good for the greatest number" but Communitarism is stress social responsibility and focusing on the whole rather than the individual. In relation to PR and associating these two theories with Appiah's I think that it would be difficult to actually determine when what your doing as a PR professional really benefits the most people. I am sure there are situations when that course of action will be obvious, but what about your public. How can one decide what is best for the most people when your public may not be included in that group? I am a little confused when it comes to putting all the theories in action. I believe and agree that in doing PR you have to do what benefits the most people for your client but what I am hoping to learn through the duration of this course is how to discern what is the best course of action for a client while not compromising self.