One size cloth diapers are a great addition to the marketplace. So, if they're so wonderful, why would anyone use anything else? The answer involves how many children you want to use the diapers for. A one size cloth diaper, used from about 10 lbs through potty training (for most children), is pretty much "used up" or worn out after one child. So if you're only planning on one child, or this is likely your last child, then one size cloth diapers are a perfect choice. If, however, you want to use the same diapers on multiple children, then I recommend getting perfect size (small, medium, large) diapers. They're simpler to use, and while it costs more upfront to buy the different sizes, you'll come out even in the long run. If you decide to primarily use perfect size diapers, you still might want to try a few one size cloth diapers. If you have more than one child in diapers, these can be a lifesaver in the diaper bag, able to be used on whichever child needs extra changes. Or if you have trouble getting a good fit on your child in a sized diaper, a one size diaper might provide the flexibility of adjustment that you need.