It was pretty easy for me to choose one size.  They do tend to be a bit bulkier because of the snap down rise, but that is worth the convenience to me.  I thought fuzzibunz were annoyingly bulky on the sides in a medium setting, so I would definitely be interested in trying a medium FB.

I stress over clothing sizes as it is.  Sizing isn’t consistent from brand to brand, sometimes you need a different size top and bottom, trying to pack up one size & get another out.  It makes me crazy!

Sized diapers tend to be a few dollars cheaper than their one size counterparts, since there is less material used.  I’ve heard many people say they were able to make due with just small and medium sizes, skipping newborn and going to trainers in lieu of larges.  Still, you’re looking at a larger expenditure for sized diapers.

With one size diapers, you can easily switch sizes on the fly, making for simpler diapering of multiple children.  It’s also nice to be able to go up a size & add extra inserts for nighttime.

I’ve also heard people say their size went down as they became more mobile/their body shape changed a bit.  O/S diapers make this more manageable.

Now, one size diapers often say they will fit at 7 or 8 pounds, but do not really fit well until 9 or 10.  If you have a really tiny baby, this can be a problem.  Happy Heinys and Rumparooz have an extra small setting, and a few companies even have a mini one size diaper that will go from birth to 15 pounds or so.  You still have the issue of steering clear of the umbilical cord stump though.  Some people just do disposables for a few weeks.  Rumparooz has a tiny all in one that fits preemie-12 lbs and has a snap down for umbilical cord care.  They have the inner gussets and they are just soooo little and cute.  I don’t think I could justify the expense, but I sure do love them!

If you have a very large baby, or a late potty trainer (learner), one size diapers may not take you all the way through either, so keep that in mind!