Comment by Uvix
"Easier to add your own books"... it depends. Yes, if you have ePubs and want to transfer files to the reader via USB, Kobo is marginally easier. But Kindle is easier for wireless delivery (regardless of format), and supports it on all of their models instead of just a limited subset.
I have KOReader on my Kobo device, with a couple taps I can connect to my desktop instance of Calibre and transfer books in a flash.
https://koreader.rocks