In the days before water conservation, selection of toilets was easy: look in the catalogs or visit a home-improvement store--then select the one that looks best, or costs least. Today the issue has become far more complicated and important. Saving water is a critical concern. Silent operation is often important, and reliability and ease of repair (with widely available replacement parts) are central issues. Appearance, of course, remains crucially important as well (expected different from an architect?). And, in the age of globalization, product choices have increased enormously, with a huge variety of toilet bowl styles, shapes, heights, mechanisms and operation. Selecting and purchasing a toilet has become a challenging endeavor.
Internet to the rescue:
Wikipedia has a comprehensive review of the history and development of toilets, and explains flushing mechanisms in great detail; highly useful because the choice of flushing mechanism often determines both the cost and water efficiency of a toilet. Although the article descends quickly into "toilet-nerdery" in its detailed discussions, there are few better sources of basic information on the topic.
Terry Love, a plumber in the Seattle area, has the most comprehensive review of toilets, including user reviews, efficiency ratings, costs and personal evaluations. The gold standard encyclopedia of toilets, the site includes a highly popular bulletin board with many public forums and hundreds of participants and contributors; topics range from toilets and lavatory sinks, to kitchen equipment and lawn sprinklers.
And for those "aftermarket" bidets which replace toilet seats (originally popularized in Japan), the Wirecutter web site has an extensive comparative review with in-depth test results.
One more: Consumer Reports has a lengthy, detailed web site discussing and evaluating high-efficiency toilets; extremely important in increasing water savings.