I prefer the school bus as they have some responsibilities to drop your child at home on time. If the driver is sick or something happenes to the bus it will be the responsibility of the school to arrange an alternative for picking and dropping your child. A private driver does not have that sort of responsibility. They might do some sort of adjustments in case if the driver fell sick or something happens to his car but still if something goes wrong you have no chance to complain and if you ask him for explanation he will tell you, ok cut the charges for those days which I did not pick your child.