One consideration I will add: We built a house recently and installed four new toilets. In the past, we had always installed the Kohler Cadet (II?) toilets, but I wanted one with a heavy-duty flusher. A well-known brand that goes into commercial establishments, especially restaurants that always flushes well and had a shiny thick glaze was making residential models, so I bought one. The plumber hooked it up outside for me to evaluate. The flush was OK, at least better than our Kohlers have been. So I bought three more. Within a short time of living there, I realized that the glazing was too thin and the interior surface was rougher, which means that you have to work harder to clean and use a lot more chemical cleaners. I resorted to bleach, which was cause for the company to reject my complaint. The last two Kohlers in another building have been in operation for about 15 years with no problems. I don't know whether there has been any trimming in quality/value with current items; when one company out-competes by trimming quality, it puts pressure on competitors to follow suit.
Whether the root of this change was economical or driven for green benefit, this will be a short-term toilet, which leaves a greater environmental impact. [It seems that the calculations for environmental footprint miss some important contributions.] So, newer is not always better. There is also a "fire clay" material that is like a poorly glazed ceramic. A heavy glaze is worth a bit more as a long-term investment, in terms of useful lifespan and cleaning effort.
So, if you go shopping, inspect the interior well. Have some fun with it by asking for a demonstration.
I do agree on a second opinion. And I like Rule #7.