If you like books, you should definitely write one instead of a screenplay. Novels are the ultimate form of art—you create a book, and that's it. It's on a shelf with your name written on it. Screenplays, on the other hand, are just one step in the long process that leads to the final creative form: a film. Even if you write the most amazing script ever conceived, it might not get made into a movie unless someone else comes along and makes it so. As for them being similar... well, both books and movies are forms of storytelling, which is why they can be such an effective way of getting ideas across to others. A writer needs to be able to imagine what it's like to be someone else in order to explain what happens in their own story clearly and entertainingly, while a viewer/listener needs to imagine what it's like to be in another person's shoes in order to understand and empathize with the characters in the movie or TV show. Books are also very portable, while films have to be shown in certain conditions (bright lights, speakers playing music when there's no one around to hear it, etc.). But beyond that, there aren't any similarities between the two forms. Writing a novel is a huge undertaking that may or may not result in anything being published, while writing a movie script isn't a full-time job and hasn't been since the 1970s. A movie can take years to make while a book can be finished in a few months.