Hi, and welcome! Congrats on your pregnancy! :)
I basically went by the reviews of other people. So many of my friends had used the playtex drop in bottles that I had to give them a try, and since my DD loved them we stuck with what worked...lol! What I'd suggest is go by what other people are saying, and buy at least 2 kinds of bottles, that way if your baby doesn't like one kind you'll have another kind on hand just in case!
Please stick around, let us know what the sex of the baby is when you find out! :)