Toto used to be one of the few brands which figured out how to make low-flow toilets which didn't easily clog and which didn't require high pressure (which is noisy). They just have a large diameter flapper.

American Standard now has this technology (but they use two standard sized flappers instead of one large one)- they call it "VorMax". I have one of each- the American Standard has a rimless bowel and is easier to clean.