At first, I wasn't sure what type of formula to buy for my 4 month old and so i decided to buy Similac infant first. I was afraid my son wouldn't like it but after his first try, he drank his bottle like a champ! Yes, he does lay out gas but its not that smelly with Similac. I then tried Enfamil but it was too much for the baby. He couldn't stop laying farts which stank! Also, pooped a lot more with Enfamil. But on the contrary, Similac seemed more comfortable for my baby.