In the past, I went through this endless cycle of switching between different lead-free formulations too. Regardless of the formulations for lead-free solder (SAC305, SAC405, Sn99Cu1, etc.) I would focus more on the lead-free offerings from reliable brands, such as Kester, Multicore, Stannol, and so on. If the work is for a hobby, then try whichever you like based on cost and ease of purchasing. If it's for business, then write to the solder manufacturer and ask for their advice.