I started by reading the manga and it seemed pretty good, the thing is sometimes the Ml can be quite annoying, but then I learnt that in the novel you can understand everything much better. With that in mind, after reading the novel, the manga is lacking in many ways, there are parts that were much better in the novel and aren't portrayed as deeply in the manga. People who hate Killian because of his attitude of blaming everything on Edith, you can definitely see a character development in the novel, while in the manga they don't show much of Kilians' pov. That does notmean the manga is bad, compared to the novel it could be way better (I also love the art style).

I recommend reading the novel if you want to fully understand the characters and the complexity they have, but as a way of spending your time, reading the manga is not a bad idea.