M.B.
I've used Dr. Brown's and Avent - bpa free plastic. (Dr. Brown's has glass now too.) I liked the Dr. Brown's very much but they have a two part vent, which ended up making my husband a little crazy when he washed bottles. So, with baby two we got Avent bottles which have been fine. The only thing about the Avent that bothered me, is that they sometimes leak from the screw collar. It doesn't always happen, but sometimes if the nipple isn't seated right it leaks. It's an easy fix but I hate when the bottle leaks. And if you're bleary it can leak quite a bit before you notice. Having said that, I like them and they have fewer parts to clean. Congrats on baby #4!