I do not know if they are the best, but there are 2 cameo places near each other on Vomero hill, near Castle Sant Elmo. They both said that they help supply cameos to the military exchanges and both have people there that spoke English. You can go to both and price compare since they are so close to each other. Make sure to mention you are military since one of them specifically says they give military discounts. Both seemed nice and one allowed me to watch them work on pieces. The trip up there is also totally worth going if you have not been up to the castle on Vomero hill, spectacular views. Hope that helps.