Which treatment works the best and fastest for anemia?

It depends. It depends on the cause of the anemia. Vit b 12 will be needed if you have deficiency of vit b12. Iron replacement is the answer if you have iron deficiency . If you are anemic due to blood loss/bleeding- then the treatment is to stop the bleeding. So, see you doctor and try to find out the cause of the anemia.
Vitamin B12. Since pernicious anemia is a disorder of the absorption of vitamin B12 because the stomach cannot create intrinsic factor-something that is needed for the absorption of b12, the vitamin B12 must be given by injection intramuscularly usually once a month.