I very consciously did not buy a Kindle when choosing an Ereader about a year ago. The Kobo H2O is incredible and has served me very well. The format support is wonderful, and the stock OS does more than I need (though there is a whole community of custom OSes that also look cool). Combined with Calibre, I don't even see what the Kindle value prop is.
One reason I'm stuck with Kindles is because Amazon makes it sane to look up words when reading Japanese books and articles.
When you use Amazon's "Send to my Kindle" service (eg, you email a book to yourself, and then it appears on your device), Amazon seems to do some kind of de-conjugation which magically knows how to break-apart terms and grammar so that you can easily look anything up. Normally, if uploading straight to your device, or if using a Kobo, a term you want to look up has to match your on-device dictionary exactly, which is clunky and awful, especially since Japanese doesn't use spaces and has lots of inflections.
If Kobo had something similar, I'd ditch using Kindles entirely.