Which do you like more screens and muffled sound, or dials and lots of sound? That’s pretty much it. Some options changed, and some weren’t available in the facelift. Other than that there were very minor changes to light signatures.
For the facelift, AMG Dynamic Plus package was dropped, along with some options like sports tyres (Michelin Pilot Sport Cup 2] and some standard features were also dropper on the GT C Roadster like active aerodynamics, to create space for the GT R Roadster.
The AMG Dynamic Plus package (code P71) adds a Race engine mode (engaged with the same rotary controller) and also added dynamic engine and transmission mounts, firmer suspension, and yellow dials (only visible indication).
If you want your GT C to be as close as possible to the GT R then go for the pre-facelift with the AMG Dynamic Plus package and sports tyres. A few Roadsters were specked like that as the GT R Roadster wasn’t anticipated when the GT C and GT R were launched (together).