I guess Algebra or Geometry because I never needed it as an adult. History helped when discussing politics and world news later in life. It also helped in trivia games. It's a good basis to have to sound well-informed.
Social Studies and History are useful subjects for life in general. If you understand what happened in the past, it will help you understand what is going on in today's world. Furthermore, even if you don't need the precise information from a subject, learning helps develop your ability to analyze, evaluate, and reach informed decisions in your life. Least useful would probably be algebra (though some tests for employment require a basic understanding of algebra.)