Welcome, Zorro's uncle.Zorrosuncle said:
I think the latter is a safer bet. When you put the SD card in the Kindle for the first time, it formats it and creates the Kindle file folder structure. If your book is not in the right place, it won't show up. In fact, some folks have had problems getting their Kindle to recognize a "used" SD (one that already has files on it).
Transferring files via the USB is easy. Plug in, use windows explorer, copy & paste. Make sure files are in the documents folder for them to show up on the home page.
Leslie