This study evaluates the performance of various germline Cas9 promoters in CRISPR-based homing gene drives, aiming to improve drive conversion rates and minimize the formation of resistance alleles. The researchers tested eleven *Drosophila melanogaster* germline promoters, finding that some achieved higher drive conversion efficiency with minimal embryo resistance but none completely avoided somatic expression. Despite this, somatic expression often did not carry significant fitness costs for a haplolethal gene target, suggesting somatic drive conversion. One promoter, *CG4415*, outperformed the well-known *nanos* promoter in a 4-gRNA suppression drive, successfully eliminating the cage population. Overall, these Cas9 promoters show promise for homing drives in *Drosophila* and may have valuable homologs in other organisms. The study highlights the importance of balancing drive conversion efficiency, embryo resistance, and somatic expression to optimize gene drive systems.This study evaluates the performance of various germline Cas9 promoters in CRISPR-based homing gene drives, aiming to improve drive conversion rates and minimize the formation of resistance alleles. The researchers tested eleven *Drosophila melanogaster* germline promoters, finding that some achieved higher drive conversion efficiency with minimal embryo resistance but none completely avoided somatic expression. Despite this, somatic expression often did not carry significant fitness costs for a haplolethal gene target, suggesting somatic drive conversion. One promoter, *CG4415*, outperformed the well-known *nanos* promoter in a 4-gRNA suppression drive, successfully eliminating the cage population. Overall, these Cas9 promoters show promise for homing drives in *Drosophila* and may have valuable homologs in other organisms. The study highlights the importance of balancing drive conversion efficiency, embryo resistance, and somatic expression to optimize gene drive systems.