Our favorite toilet is the Kohler Pressure Assist 1.0 gallons per flush. This toilet carries the highest MaP* test rating of 1,000 grams per flush. It does this with only 1 gallon of water, a great water surface area, and great bowl washing. This toilet comes in a standard (Wellworth) and adult height(Highline) models. It is not available with a round front bowl. It is available in a one piece as well (San Raphael)
If you need a round front bowl, we recommend the American Standard Cadet 3 Flowise. It is available in both heights as well. This toilet also has great water surface area and bowl washing. It also has the highest MaP* rating.
What about Toto? Toto toilets are good products and many people like them. However, the top performing Toto's only get an 800 on the MaP test. Some have very small water surface areas and as a result don't rinse well.
And what about dual flush toilets? I put in very few dual flush toilets. A dual flush toilet (0.9/1.28) will average out to about 0.95 gallons per flush for the average person. I prefer the pressure assisted flush toilets instead.