I own a Glo and am awaiting my new Kobo Mini. I used to own a Kindle 3G 3rd gen but lost it- (still sad about that- I really loved that reader). I bought a Paperwhite and a Kobo Glo to try out both.
The Paperwhite won as far as speed and some aspects of the software. But it had half the storage of the previous version (really, Amazon?
) and no SD card slot. With my large ebook collection that was the main reason I went to Kobo.
Kobo wins hands down with the backlight. I found the unevenness along the bottom of the Kindle's light to be quite distracting and uncomfortable. The Kobo light is second to none.
As far as the software interface it's pretty much a tie in my opinion. There are aspects I like of both.
Besides all this I'm also a proponent of free and open source software and I am glad to be running a device that doesn't use a proprietary format as well.
I recommend the Kobo, personally.