Sometimes questions like these seem trivial or silly, but they can weigh heavily on a cloth diapering parent about to invest hundreds of dollars in diapers. Snaps and velcro (also called aplix, hook and loop, touchtape) are both equally popular for diapers, and parents' needs usually determine which one they pick.
Snaps are great for durability and laundry. With no laundry tabs to worry about and nothing to snag in the wash, they are great for just tossing in the machine. They don't lose stickiness, are good for children who become diaper Houdinis and are great for trim side-snapping diapers.
Why not snaps, then? Velcro is better for adjustability, since you don't have to rely solely on the snap positioning to get a good fit. While snaps aren't hard, many people who are hesitant to cloth diaper and many caregivers lean towards velcro since they mimic the function of disposable diapers more closely.
For our stash, we have a mixture of both. I don't really prefer one over the other, and I like trying new diapers too much to exclude a whole class of diapers from testing :)