These things are commodities these days. Probably of more importance is the build quality and the flash memory chips used. Chances are any brand will do the business.
The Toshiba appears to be able to store bookmarks. I suppose this would be a good feature. Is the KingMax capable of storing bookmarks?
I'd buy the cheapest available, make sure to backup and in the unlikely event of having problems just buy another one.
Bear in mind that any flash device has a limited lifespan since the number of write/erase/rewrite cycles is limited. It should be in the 10s or 100s of thousands but do be aware that given enough use the device will eventually experience write errors.