Since I've started CDing, the number of one-size diapers on the market has greatly increased. The might look a little different, but all of the one-size diapers have the same idea: more bang for your buck. Since it can be such a money saver, why would anyone buy sized diapers? Isn't one-size the logical way to go?
I do love one-size diapers. I find them particularly convenient for the diaper bag. Whichever daughter I am changing, I have a diaper that fits. It really cuts down on how many diapers I need to carry with me. It's also great to know that when your child is ready for the next size, you have a stash ready to go.
Bum Genius were the first one-size diapers I ever tried, so they hold a special place in my diapering heart. I find them easy to use, relatively trim, and well-fitting. Some have had problems with the elastic and velcro. We've been lucky with ours though, and some are going on two years of use.
Mommy's Touch diapers are well made and long lasting. There are only two size settings though, so this may be a better option for small-large sizes rather than starting at newborn. The snaps give a trimmer fit, but for some the system is too complicated. The aplix is easier, but just a shade bulkier.
Happy Heiny's One Size are very nice. The aplix stays nice and flat for us, but there is a snap option as well. Like the BumGenius, there are two inserts included.
Tiny Tush is also a well-fitting diaper with snap and aplix options. The foldable insert gives the ability to customize absorbency where it's most needed.
Are one-size diapers really good from birth until potty training? I guess it depends. Personally, I felt most comfortable with one-size diapers around 9 pounds. Before then, I just felt they were too bulky and preferred newborn diapers. Others have no problem using them from the get-go. It's really a matter of preference.
As for how long they last, it really depends on the size of your child. The weight ranges are different for each style. I've found the the rise on Mommy's Touch is higher on my older daughter than the other styles. My older daughter can still get away with the middle setting of the other diapers at 2 years and 25 pounds. Other babies at this age have already outgrown the largest settings by this time. To determine which diaper is best, try a few out before committing to a whole stash.
Much of the point of using one-size diapers is saving money by buying diapers once. Some complain that their diapers don't last the whole time they are needed. This advice isn't foolproof, but it's what I've found to be helpful:
When it comes to one-size, the dryer is not your friend. We have no issues with the PUL holding up, but find that frequent dryer use is not good for our elastic (not just for diapers, but all of our clothes actually). If you use the dryer, use it on the lowest setting. Pockets only need about 20 minutes to dry if that, so take them out as soon as they are dry. Don't stretch the elastic until it's cooled. To maximize elastic life, try hanging your pockets. They should be dry in a few hours.
So what's best? Why buy sized? For us, we use a combination of one-size and sized diapers. Sized diapers are trimmer and it's possible to get a better fit with a more customized size. We do use one-size about half of the time. I don't think I'd want a stash comprised entirely of either. This may not be a definitive answer, but it's really hard to give one. Go with what's simple for YOU!