what size diapers should I buy and how many?

When a baby is born, what size should I buy?
There's newborn and than there's size one right?
Should I buy two packs of the newborn and two of size one?
I guess my main question is, how fast will the baby grow?
That way I know how many packs of diapers I should buy. 
Ps. What diaper do you recommend for newborns?