I think Attack on Titan and it's not even close, Demon Slayer doesn't come close to Attack on Titan when it comes to storytelling, the fights as well. Obviously you can say that animation is better in Demon Slayer but I think that's pretty much the only thing that Demon Slayer has over Attack on Titan. Attack on Titan's animation is really good too. If you see Levi's chase scene with Kenny, really good animation, really good story line, much better. much about it's not even in the same hemisphere when it comes to story