The Define C is shorter depth wise than the Define S. The latter has support for really thick front radiator placement or push/pull setups, provision for 3x3.5" drives behind the motherboard tray while one is missing on the Define C. SSD support is one more than the Define S in the Define C. PSU shroud in the Define C, not the Define S.
The last glaring difference is the ability to buy an matx version of the Define C while the Define S only comes in mitx(Nano) and atx.
It's more about what the case can do for you rather than looking at pros and cons since each build will have a different layout and ofc a different appeal and scheme/theme. You'll be greatly served with any of the two but if you lack depth in your computing space or the desk, to be exact, then the Define C is the case for you.