Mostly, it comes down to personal preference. There are some pros and cons that I can highlight for you, however, that might help you make an informed buying decision.
APLIX
Pros: I have always felt that you can get a more customized fit with velcro. No "between-snaps" size. I have heard others say that the fabric doesn't wear as badly around velcro tabs as around snaps, but I haven't experienced this firsthand. It can also be easier for caregivers to use -- no remembering which set of snaps to use.
Cons: Velcro can curl over time, lose its sticky power, and some children (like my youngest) can learn to undo it more easily than snaps.
SNAPS
Pros: More durable. Snaps never lose their hold. More difficult for little hands to undo.
Cons: More likely to be "between sizes". Takes longer to do than velcro. Can be more confusing for caregivers. Sometimes causes wear on fabric.
All said and done, I use both. Velcro BG 3.0s on my big boy, and I've switched to snap Best Bottoms for my little one as he learned how to undo the other covers. They each have their merits, which do you prefer??
