Consumer Reports rated toilets in an issue last year. Interestingly, they found the single flush toilets rated generally higher than the dual flush ones. And Kohler didn't fare that well, nor did A/S.
Over this past winter I replaced the stylish vintage A/S Carlyle low-boy (about 1964) in the master bath with a Water Ridge one-piece dual flush from Costco. I've been pleased with the WR. It uses 1.1/1.6 gal, you don't have to hold the buttons down, and flushes as well if not better than the vintage A/S did. And uses a lot less water in the process. I'm probably going to replace the pink no-name 1941 era commode in the original bathroom with another one-piece WR. I've put it off a bit because it will probably require a new shutoff valve at the wall. But since the pink one no longer flushes properly (you have to hold the lever down, and then it takes a while to decide to start refilling the tank afterward), it's probably no more difficult to replace the entire toilet rather than put in new valving.
