One thing to keep in mind about velcro vs clips is the chassis flex. Velcro will affect the chassis flex (typically will stiffen the chassis a touch), this could be good, bad or indifferent depending on your driving style, setup and track conditions.

I run velcro only on the sides. I cut the nubs for the clips off and put the fuzzy velcro there just to keep the body from getting too scratched up on the inside.