Synthesize the different types of "service through writing" discussed and rank them according to their spiritual efficacy as described in the source.

The preface in Chapter 0 outlines a hierarchy of service through writing based on spiritual effectiveness. The lowest form is writing biographies of worldly leaders, which is considered a worldly service rooted in self-interest and does not yield spiritual fruits. A higher form is writing the biographies of many saints; this is considered a form of Guru service that yields spiritual fruits but is still partial and insufficient for the ultimate goal. The highest and most certain service for attaining salvation is described as writing the biography of one's own Sadguru, preferably in a detailed poetic format, and engaging with it through dedicated study, Parayans, and Saptahs with unwavering devotion.