i have a cybook, but the screen and e-ink display is the same as the kindle - and i recommend it highly
the sony is lower in price, but the main thing to consider is which fomat has the most books that you'd actually like to read. with kindle, you can only buy ebooks at amazon, although they do have a great selection, but you can get some for sony readers if you get the multiformat versions of the books at
http://www.fictionwise.com and with cybook you can read mobipocket ebooks you can buy at places like
http://www.booksonboard.com www.mobipocket.com and
http://www.fictionwise.com/ , and a bunch of other stores.