The scar can be hidden if you wear a closed shirt or a coat, but the broken horn cannot be hidden, it will be broken for the rest of your life or you will have to tape it like Jack. Kaido will always remember Luffy when he looks at his own face, his identity has been tarnished, he will be uglier than natural thanks to Joyboy Luffy. Morally speaking, the broken horn must be worse for Kaido than the scar, and physically it must have hurt more since the horn is a bone, and Zoro's cut was on the outer skin. The pain of a fracture must be greater than that of a semi-superficial cut that soon heals.
But, the scar was nicer because the framing was much better, since this framing of Kaido losing his horn was very confusing, the broken horn became just a detail of the total.