BunjinEnt

Without diving into a thesis on "Zen and the Art of Motorcycle Maintenance", the clays from areas in Japan and China have desireable color and workability and fireing properties that potters have been using for centuries. Ceramics in those areas have been made by families who have been passing down the art and craft for generations. The quality of the pieces or (more likely) the price of the pieces depend on the way in which they are made and by whom they are made. Mass produced pieces would tend to have less value than hand made pieces. They would tend to have fewer flaws than handmade, but the flaws are what give unique pieces their character. As is the case of handmade 100% silk carpets from Iran. The weavers actually add flaws to prove they are hand made.
It kinda goes back to the "What is Art?" question. Art from certain folks commands higher prices than others.
If you are interested, there is info out there on who the big name pot makers from Asia are and what their chops look like.
As a rule of thumb (this is kind of a no brainer) the pots with stickers (Made in China) tend to be inexpensive and of lesser quality whereas the ones with chops and stamps designate specific pot makers or factories.
I don't think certain clays once fired to stoneware temps, have any special properties than any other clays. There are only the differences in the properties for the formation and decoration of the pot by the potter.

A rule of thumb also is to stay away from earthenware fired pots as they tend to crack over time due to the freeze/thaw cycle of water and porcelain as the clay is too vitrified to add surface water retention or root grip inside the pot. But I have seen some very nice pots from both categories...

Hope this helps,

-Wm