Blaptica dubia takes a long time to grow, so they are good if you're planning on buying a large number and just keep them until being used as food. They are also so very much more nutriocinous than crickets. However, dubias are so easy to breed, you might as well if you are already going to buy a large amount.
Lastly, it'll probably be cheaper to buy from from a private person that breeds them, instead of a pet store.