The best for anyone who is sexually active, unmarried and not trying for a child, is for
the female to be on some form of birth control (
the pill,
the IUD, or Norplant)
AND for
the male to use condoms. Not one or the other. The pill, IUD, etc. will prevent pregnancy but not disease. Condoms will help greatly to prevent disease (given that they are used properly) but are not considered 100% for preventing pregnancy.