Definitely the Kindle. Amazon offers an amazing service, especially their personal document service's email feature. That is simply divine. Furthermore, Amazon isn't nearly so annoying to use as a non-US citizen. I don't have to use a trick credit card or proxies to purchase ebooks. Amazon just sells them to me, easy peasy.
Disclaimer: I have a first generation Nook and a Kindle Touch. My comments above are however entirely based on the services provided, not the devices themselves. So this is probably more appropriate as Barnes and Noble vs Amazon.