S is the sportier of the two; blacked out trim, sport seats, black headliner, blue stained dash wood trim. The C is more "mainstream luxury" and has a lighter interior, and technology package (stop and go ACC, Lane Keep Assist, collision mitigation, etc.). Not sure if panoramic sunroof is available on both or just C. I would check for you, but only have my phone right now.
From the outside you would be hard pressed to tell the difference, if they both had the 19" wheels. The S was released with a bunch of info about how the AWD acts more rear biased when in sport mode, but honestly can't tell you if that's different from the C.