Only bottle the baby will take. My g baby had all kinds of expensive bottles and nipples. Advent dr brown como’s, lots of parts in some of these .. I wanted playtex because that’s what I had for my kids, but they really don’t have these any longer and they are $$$$. I’m a nurse and worked with babies a long time ago when Nuk first came out. Most baby’s rejected the nipple, bulky, but these are a new design, slimmer, easy to wash and sterilize in a machine not a lot of cumbersome parts and reasonably priced . I think bottles now days are just a lot of bs smoke and mirrors . Remember in the hospital they used Nuk or standard ready to feed nipples?? Ok so a few babies have colic most don’t and IF you burp frequently and properly then there should be no issues.Our baby takes Nuk great and loves them. Oh and easy to handle too! Plus a little vent on top and they DONT leak. Save yourself a lot of trouble and expense. Keep it simple and you’ll be fine. Billions of babies born don’t need fancy tricks just good clean functional equipment until they grow to the next thing! Thank you Nuk !!