Sorry I can't directly answer your question about the different types of Sportster seats; but what I can do is relay my experience with the several types of seats that I have tried>
Of course my first experience with a Savage seat was the stock seat on my 87, and we all know how terrible those are. Raising it did improve it considerably, but not nearly enough.
Next I tried the "stock" Sportster seat which still resides on my 87. It is indeed a decent improvement over the stock Savage seat; but for my nearly 6' and 250+ pounds it still keeps me pushed too far forward for real comfort.
Then I bought my first 99 model, and it had what appeared to be a "stock" old style Savage seat; but upon close examination it appears much more curved or "dipped" than original. It seems that someone had previously modified it; not by adding material as one might guess; but by cutting foam or removing layers somehow making it almost an inch thinner.
I've not taken the seat apart to see exactly what was done to it. Amazingly, this modification made the seat comfortable for 2-3 times the distance of the original configuration. At some point in the future I may disassemble that seat; remove a bit more material and add a thin gel layer in hopes of improving it yet more. As it stands it is my most comfortable seat of the three... I have on my three Savages.
There is a custom re-upholstered late model single piece S40 seat on that first 99. That seat looks a lot like the ones you see on a lot of the German bikes. I have since bought another 99 which now has the modified stock old style two-piece on it. Until I get a really comfortable police style solo seat on it, as a "road" bike, I expect that seat will remain the most comfortable I have.
Addition: BTW, here is a link to a German maker of rather expensive alternatives.
http://www.gts-seats.de/english_index/programm/suzuki/modell/SUZUKI_LS_650/in...The seat on my "chopped" bike was bought because it reminded me of their "Cobra" seat, and I got a good deal on it!