Bottle brand and material get most of the attention in marketing, but nipple flow rate is the detail that most directly affects whether a baby feeds comfortably.
Flow rate is sized by stage, not just age on the box
Nipple flow rate — how quickly liquid passes through when a baby sucks — is generally labeled in stages (often numbered or described as slow, medium, fast) rather than a single universal size. A flow that's too fast for a baby can cause coughing, gagging, or milk spilling out around the mouth, since liquid comes faster than the baby can comfortably swallow; a flow that's too slow can lead to frustration and excessive effort for the baby to get enough milk, potentially causing them to feed inefficiently or take in extra air while working harder to feed. Age ranges printed on packaging are a starting guideline, not a guarantee — some babies do better on a different stage than their age would suggest, and watching how a specific baby actually feeds is a more reliable signal than the age label alone.
Material affects feel and durability differently
Silicone nipples are soft, flexible, and generally considered to feel closer to breastfeeding, and are more resistant to damage over time. Latex nipples are softer and more flexible still, but degrade faster with repeated sterilizing and exposure to milk fats, and pose an obvious problem for a latex allergy or sensitivity. For bottle bodies, glass doesn't retain odors or stain, and doesn't leach anything into contents, but is heavier and can break if dropped; plastic is lightweight and shatterproof but can degrade with repeated heating and sterilizing over time, and it's worth confirming a specific plastic bottle is BPA-free, which is now standard in most markets but still worth a quick check for older or secondhand bottles.
Anti-colic features are a real design category, not just marketing
Bottles marketed as anti-colic generally include some form of internal venting system designed to reduce the amount of air a baby swallows while feeding, which some parents find genuinely reduces fussiness and gas — though babies vary individually in how much this actually helps, and it's not a guaranteed fix for every baby's discomfort. These systems typically add more parts to clean, which is a real tradeoff against the potential comfort benefit.
The one thing people forget
Have a couple of different nipple flow stages on hand rather than buying an entire large set at one single stage, since babies typically need to move up in flow stage as they grow and get more efficient at feeding. Buying a large supply at a single stage often means replacing much of it sooner than expected once a baby outgrows that flow rate.