Have worked as a ROM developer for 10+ years. Amlogic would be the most familiar SOM to me as I contributed to a Canadian IPTV company who were operating aml based IPTV system. Aside that, I have good experiences with Rockchip, Qualcomm, MTK and Rockchip as well.
Basically, I was doing Linux firmware for Amlogic, and I was first one to put Kodi Linux on s8xx and m6 SoCs way back, then I built my own firmware called Ember which we sold to a couple companies and licensed to users if they wanted premium features.
I can build you a custom ROM along with any desired features like a dedicated Launcher, a custom boot logo, an OTA update solution, and many more.