I haven't used either, but I'm 39 weeks pregnant and was hoping to try out both systems once the new baby gets to be a couple months old (I have newborn fitteds that I like, and I hate the way one-size diapers fit a newborn, even a big newborn).
I looked into both more closely and bought a few Gro Baby diapers this weekend--I think that system seems more promising, so I decided, rather than trying both, to try those and see if we like them (and only try the gDiapers if I *don't* like the Gro Babies). Here's why I think I like them better:
--They're one-size, so I can buy one set of covers that will last for the whole diapering-period. I've talked with people who are using them on 35 pound 3-year-old (both my kids were potty-trained before 2, so we shouldn't *need* them to fit anywhere near that size--except if we want to use them for bedwetting protection later, I guess), and someone using them on a 12-pound infant, and they both said the fit was great.
--I like that the whole cover (and not just a snap-in insert) is waterproof. They seem, to me, less apt to leak for that reason.
--The inserts seem more absorbent to me, although I'm just judging by looking.
--I like that I have the option of snaps or aplix. I bought two aplix and one snap cover to start out, because my husband prefers snaps and I...am undecided, but I think I like the aplix better, at least while they're little.
--Also, I'm not sure if this has been mentioned in this thread or not, but I learned when purchasing these that Gro Baby will soon be releasing a disposable insert, fully bio-degradable (not unlike the gdiaper--although I don't believe they bill it as "flushable," I've heard the gdiapers may not be as "flushable" as they seem and have been rather hard on some people's plumbing). This was one big draw to the gdiapers, because I thought it would be nice for travelling (we often have to buy disposables when we travel, so this would make a nice alternative), but it appears that the disposable inserts will be an option with either system.
Like I said, I don't anticipate really trying these out until the baby gets to be a couple months old--I used bumgenius pockets on my daughter, and I hated how they fit her as a newborn (and she was 10.7 at birth). Once she got to be about 2 months old, though, they fit her nicely--but I'm pretty excited about them. They seem really well-constructed to me, and simple. I'll let you know if I'm wrong on either account.
