Samsung - Exynos Development Board

Look for used "Samsung Artik" modules on eBay. They are the older, IoT-focused Exynos chips with slightly better documentation for the tinkerer.

if you want to build a product that actually goes into mass production, the Exynos dev board is your blueprint. It is expensive, loud (the fan is massive), and powerful. samsung exynos development board

Have you developed on Samsung silicon? Let me know how you handled the bootloader headaches in the comments below. Look for used "Samsung Artik" modules on eBay