Use the adjective sapient to describe someone who always gives the smartest advice, like your brilliant, insightful teacher or your wise little brother.
Calling someone sapient is a compliment, since it means "insightful and wise," although it's often used in a sarcastic way: "My sapient adviser said I should major in Communications." The phrase "sapient life forms" shows up frequently in science fiction, as well. The Latin root is the verb sapere, "to be wise," which is also the origin of sapiens, "wise man," as in Homo sapiens, or the human species.