I always look around when we're about to be out and see who has them on sale. I did diapers.com when I had the $10 off coupon but now they seem to be a little higher then what I can get elsewhere. I compare publix, target, bru. Sometimes BRU will have $5 giftcards if you buy 2 boxes which we go through that in a month usually.
I will warn you don't buy to many newborn diapers until you're baby is here and you see how big they are. We never used newborn diapers and had to give away a ton of them and DS was only in size 1 for about 4 weeks before we moved to size 2. I had to take back about 2 boxes to target after he came to exchange them for size 1 and 2 diapers.