Books have ideas that can change the world, change your perspective, and change your life. Art is nice, but it doesn't seem to have as much power over me.
Of the main forms I'd say literature > music > visual arts. Literature is the only form of art that can be musical (such as the shi, ci and qu in Chinese poetry) and visually appealing (referring here to writings that depict scenic beauty, etc.) In addition, books are more flexible: They can spell out everything, or hide the author's intents in corners - it's up to the author and that's what makes reading a joy.
As as art teacher I chose fine arts, however do we really need to choose? Many visual artists throughout history have written books. This just seems like a poll that tries to compare two things that both have their own value.