Only one: Availibility.
I don't care about any other factor (well, other than price of course
, but still it's not a major factor).
I can buy books from Amazon and remove the DRM to any other format with Calibre.
Music, annotation, or touch screen is just a nice feature not required
Currently there is only one vendor that distribute ebook reader in my country. It's Onyx Boox with about US$ 350 price tag
.
So I'm really glad when I came across my fellow countryman that sells his prs-300 for US$200 and I've just purchased it three weeks ago. After Kindle 3 is out, there is one particular electronic store that sells it here for US$333 (kind of regret my purchase when I see it in person and the Kindle is indeed a very good reader).
(Just realized the question posted in Kobo forum, well anyway just a rant from me)