What is the best treatment for headache ?

Depends on the cause: There are many different causes for headaches including stress/tension, migraines, lack of sleep, dehydration, infection, etc. Depending on the cause, different treatments can work. In general, something like Acetaminophen (tylenol) or Ibuprofen over the counter can be tried.

Best for whom?: If you mean what is the best treatment for YOU, there is no answer for that. Only way to know is to try it and see. If you are having severe headaches more than once a week, see your doctor. Your question is only the beginning of the process of diagnosis and treatment, not the end.