I get asked this question so often. a psychiatrist is the most highly qualified, having done a full medical training plus psych training, but is inclined to look for medication solutions maybe too often, and is usually not specifically training in marriage counselling. A psychologist cannot prescribe drugs, and thus relies on talking treatments, and is usually capable of marriage counselling ; a social worker similarly, though with lesser trainiong. For marriage counselling, best to start at the other end --- look for someone trained in and concentrating on, marriage counselling as such, suich as the people recommended by FAMSA.