They should be hard enough that you can't scratch them with a stainless steel fork; and strong enough that they can fall off a balcony onto a concrete patio and not break; and you can use them in a microwave oven and they won't ever be affected by the heat.
When I was a child, we had Melmac, a brand popular in the 40's and 50's. They were indestructible. Microwave wasn't an issue back then. Corelle, manufactured by Corning, isn't as sturdy as Melmac but they are durable. When dropped they don't break. The can stand up to the microwave.
Corning Ware. They have a variety of patterns. Never dropped them onto concrete from a balcony but I have dropped them from the kitchen counter onto ceramic tile floor many times.