The book that made you fall in love with reading.
Probably something from the Babysitters’ Club. Though now I recognize that they are not very good, in elementary school I loved them. I remember ordering them each month from the Scholastic catalog (or however frequently the catalog was issued) and eagerly waiting for them to be delivered to my little hands. I remember being overwhelmed by the body of work Ms. Martin created and doubting I would ever get a chance to learn all about Kristy et al.’s adventures. Then I remember being annoyed by it all and wondering whether they would ever get out of middle school.
NB: This is not the same as saying these are the first books I fell in love with. I don’t think I ever fell in love with one of the BSC books, though I loved reading them generally.