What is one of the best medication to treat type 1 bipolar disorder?

That depends: If the person is acutely manic than an atypical antipsychotic may be a good choice. Mood stabilizers are helpful for long term treatment. Different people respond better to one drug than another. It is very individual. Many of my patients are happy with Lamictal as well as abilify (aripiprazole). But that doesn't mean they are the best.