Monster, Kami no Kodomo Recommendations
These two are so similar that you could make a review synopsis of one via finishing the other. Monster is of course longer and doesn't go into the creepy artwork until the latter arcs while God's Child totally relies on it to deliver the horror. If you can stick to only one, I would probably go with God's Child but as mainstream rating already decided - most would probably head straight and prefer to read Monster rather than pay any attention to God's Child (as of this writing, I was the only one who submitted a review)
The main character of "God's Child" and the main villain of "Monster" have very similar characteristics. They are both sociopaths and nihilists, who use their charm to convince others to do heinous crimes for them. In both manga, these acts often go unpunished due to the characters' ingenuity, as well as due to the fact that there is no real motive behind them. Apart from the characters, both manga create an atmosphere of suspense and deal with disturbing and taboo themes related to serial killing and psychopathy.