If you're only looking for the hardest watch to scratch, get the black SS. Although, some managed to do it, there are many threads that talk about how hard it is to scratch. And of those people who managed to do it, the majority of that few seemed to be talking about marks on the DLC link band, rather than the actual watch body.
I've heard the SS body scratches easier than the sport.
However, that's not important if the SS is the one that looks best to you. You're going to be looking at it every time you want to check the time, so don't buy the wrong one