They are quite similar, but the Supreme uses the Unifit adapter which is a different way of installing the toilet. This adapter is quite useful if you are installing the toilet on either a 10" or 14" rough in. (The standard rough in is 12".) This means the toilet will set properly on any of the 3 rough in flanges. The Carolina is for a 12" rough in, but would install OK on a 14" rough in but would leave an extra 2" between the toilet and wall. Installation of the Unifit costs more than a conventional toilet. All of the other features of the toilets seem comparable. You can see the specs on these toilets by following the "Toilet Review" link at the top of this page, then "Shopping" on the following page, then "Toto". Scroll through the various models to find your choices. I think either toilet would be an excellent choice.