Back in high school, a friend of mine said, that she always knew I was her friend because when I asked her this question of yours, I would stop and listen to the answer. So... I learned that my ability to listen was considered more important than the actual question.
On a lighter note, I like my dad's answer to this, he says in a booming voice to all within hearing distance, known and unknown folks included: "SUPER and GETTING BETTER!" He gets excellent service in restaurants, gas stations, you name it! and lots of smiles too.