During spermatogenesis, Follicle Stimulating Hormone (FSH) primarily stimulates Sustentacular Cells (also known as Sertoli cells) in the testes. These cells provide support, nourishment, and a conducive environment for developing sperm cells. They also play a role in the regulation of spermatogenesis and the formation of the blood-testis barrier.
So, the correct answer is: Sustentacular Cells.