Spirits are the spirits of once-living beings from anywhere within the 3 Realms and Living Entities are still alive on their respective Realm. In this regard they do differ in their presence as based on their individual species, and in terms that spirits are not still living out their lifetime and their life's goals. You will find that the energy and presence of a spirit and Living Entity of the same species is different in some ways and similar in other ways. It's really a choice of companion that makes you feel the most comfortable.