From a comparative review on the web:

But assuming Kobo’s inexpensive reader does become available soon, why would anyone consider choosing it over one of the big brands?

Its open platform, for one thing. It’s got out-of-the-box native support for a variety of e-book formats including ePub, PDF, Adobe DRM, JPEG, GIF, PNG, TIFF, TXT, HTML, RTF, CBZ, and CBR. And the Kobo app lets you access your e-books across multiple devices, including PC and Mac computers, iPhones and iPads, and Android and Blackberry mobile phones and tablets.

That would decide it for me. No way am I ever buying anything from Amazon in any case. Even if it has lower build quality than the others at the same price, it looks like the Nook and especially the Kindle are not going to able to display the documents I want to seee at all. A better interface to stuff I don't want isn't much of a selling point.