One thing that bugs me about Kohler, American Standard and Toto is their chintzy glazing. On the models I examined, all were unglazed on the underside of the rim. You can feel that is rough by running your finger under the rim. I think that glazing in that area keeps it cleaner, and it is easier to clean.
I was also disappointed about the poor quality of the ceramic molds on one particular model of American Standard (made in Mexico). All of the samples I examined had substantial "flashing" around one of the mounting holes from the tank to the bowl. It caused the rubber washers or seals to not mount evenly. I was afraid that might lead to leaks down the road. I could have ground off the excess ceramic with my Dremel, but why should I? I purchased two; both had the same problem so I returned them.
At Lowe's, they carry a brand called Penguin, which is made in China. It is an inexpensive toilet as compared to the name brands, but I was impressed by the quality. The underside of the rim was glazed, as was the inside of the trap. I purchased one and it has given us good service for a year now.