As a part-time tinkerer and full-time developer, I have been fascinated by single board computers (SBCs) since the first Raspberry Pi was introduced almost a decade ago. I have owned and used every generation of Raspberry Pi, in addition to most of the popular competitors. You can search my site for tons of articles on these experiences.
One thing that is almost universally true (at least as of 2019) is that the most common system boot device is a microSD card. SD cards in general have performance characteristics that pale in comparison to faster devices, like NVMe SSDs, eMMC, and XQD or CFexpress.