probably Fairy Tail. it was my "gateway manga/anime" and led me to my manga and anime obsession, which is over now. i do still read the ongoing manga i subscribed to back then, and every once and a while i watch a bit of anime again.
i dont read manga but anime counts right? since a lot of anime are adapted from manga. anyway, mahou sensou (magical warfare)
was the worst manga adaptations ive ever watched. a lot of stuffs left unexplained on the last ep. it was slow as well.