Which pacifier should I choose for my baby?

WHAT A PACIFIER IF... EXTRA-SLOW (XS) SLOW(S) MEDIUM (M) FAST (L)
My child is premature or the Slow flow (S) nipple is too fast.
My baby is newly born or breastfed        
My baby drinks formula or thickened milk
My baby is drinking thickened milk, cereal or the Medium flow (M) nipple is no longer fast enough