I don't have a strong preference either way. Velcro gives you the option of a better fit, but snaps have worked just fine for us. DD has started to figure out Velcro, so we only use it if she's going to be in a sleeper or a onesie.
I waited to start my stash until my LO was about 4 months old and by that time BG had come out with the snaps. I decided to only buy snaps (in that and other brands) because I had heard from other momma's that the velcro needs replaced over time (important if you plan to use for future kids) and that eventually they learn to take off the velcro. The snaps take about a half second longer but they're just as easy, but I don't think they're easy enough for a child to remove.
T just won't sit still and velcro helps immensely. She's only 7 months old and pulls of velcro and snaps so I decided to go with what is easiest for me. I also had no trouble getting a good fit with snaps.
Re: Diaper Closures
Our crazy, wonderful life
I generally prefer velcro, because I have trouble getting a good fit with snaps (DD is chunky, but has a narrow waist.)
I do , however, like side-snapping diapers a lot.