What is the best placement of the placenta?

Anywhere . As long as it is not near or over the opening of the cervix or not over the uterine scar if you have has a previous csection.
Not over cervix. The placenta can be anywhere inside the uterus. The location is not particularly important as long as it is not covering the cervix. This is called a placenta previa. If a previa is present then the baby will need to be delivered by c section.