Which pacifier should I choose for my baby?

WHAT PACIFIER IF... EXTRA-SLOW (XS) SLOW (S) MEDIUM (M) FAST (L)
My child is premature or the Slow Flow (S) pacifier is too fast.
My baby has just been born or is breastfed
My baby drinks infant formula or thickened milk (before 4 months)
My baby is over 4 months old and drinks thickened milk, cereals or the Medium flow pacifier (M) is no longer fast enough