So ladies,

I'm looking for bottles to add to my registry. I've heard avent are the most liked. However, what size do I get? There's newborn, 9 ounce, 4 ounce, anti-colic newborn, wide neck stage 1... how do you choose? What's the benefit of getting a 4 oz. bottle versus a 9 oz. bottle? I know 3-4 month old eats more than a newborn but couldn't I just get the 9 oz. bottle and just put 4 oz. in for my newborn? Hope you guys have some answers for me! Thanks.