Your Health Care Representative will start his or her job of making medical decisions for you on the event of your incapacitation. It is important to choose someone who can be available locally to meet with your health providers in person to represent your wishes. Therefor for this position, many individuals choose their spouse.
Whomever you chose, it is important that that individual share your basic values as to healthcare, and is strong willed enough to stand up for what is your point of view in the face of other who may not agree with what he or she knows to be what you would want.