Not sure what an advance directive is in Oregon or want additional tips? See http://www.mgmlawyer.com/what-is-an-advance-directive/
Any time you pick a representative, it should be someone you trust. It can be tempting to choose multiple trustworthy people like two of your children, but is almost always better to pick a single person. If there is ever a disagreement about what you would want, there can be legal fees, court hearings, and other lengthy processes and meanwhile your health care wishes or end of life decisions may not have been honored.
Pick a single trustworthy person, express your wishes to them directly, make an Oregon advance directive stating what those wishes are, and deliver that document to your doctor, hospital, and health care representative. Open communication makes this process work better if ever you should need it.