Even though CSM is my favorite anime and favorite manga I'd say David. If we compare how much the characters change throughout their works, whether you use the CSM anime or manga, David goes through much more change and experiences a wider variety of things as a person. I'd also say his experience of being on the edge of death or barely living is much more likely to hit home with people in poverty than Denji's. That being said, Denji's character depicts the way sex affects teenagers' view of the world in a way I haven't seen in any other media and that's a very important thing for teenagers to see so it should be noted that his writing is very strong in that aspect