I like the idea of kobe and I heard there's good ereaders from Sony too. However amazon and kindle is easier since I'm already into the amazon ecosystem with prime.
With kobe, are they linked to Barnes and Noble in America? Can you load kindle books or is it a complete break? If tied in to B&N is that much different to kindle in that even kindle can display other formats such as free to access pdf books.
Borrow box is annoying with the kindle though. If or when my kindle goes again I might look at other ereaders. Mind you I do have some expensive books on kindle that I really don't want to have to buy again so perhaps the benefits need to be greater.
BTW with prime you get free books and some are actually best sellers too