Are all forms of biographical writing considered equal as a form of Guru service? Please explain the differences.

No, not all biographical writing is considered equal. The preface in Chapter 0 outlines a hierarchy. Writing biographies of worldly figures like politicians or warriors is a worldly service with fruits limited by time and space, and it does not yield spiritual benefits. A higher form is writing the biographies of many saints, which does yield spiritual fruit but is considered partial. The highest and most certain service, as stated in the text, is writing the biography of one's own Sadguru and studying it with devotion, as this is believed to grant the ultimate fruit of salvation.