The NOOKColor didn't appear on your list and it is more expensive but it is superior to all of the devices on your list. Better PDF support than each one, excellent organization abilities. You can arrange books in the order you wish on a shelf. It also has an excellent dictionary, notes and highlighting that are very easy to use due to the full touch screen.
It has excellent support for multiple formats, library reading and multiple DRM sources. The only big issue is that I wouldn't get one if I were in Canada due to geo-restrictions. And that is a BIG issue.
The Kindle is way to big brother for me. It reports on your location via whispernet, it gathers statistics and reports them back and Amazon has used it to removed paid for books from customers devices. So not only is the platform linked to older and less capable formats (MOBI), it is proprietary hw and sw (vs Andriod), it doesn't have any SD card support and it doesn't respect your privacy or your ownership of bought and paid for media.
The Sony issue is similar to that of Apple, you will never or very rarely see any price discounts. The price tends to be high for the features and the devices tend to be proprietary and interoperate only with Windows and Macs with current SW. Linux users such as myself tend to be left in the cold. They also don't have a simple way to shop from the device.
The Nook series of devices are much more open and SW development has been constant on them. I am a fan. But living in Canada I would probably be tempted by the Sony devices due to the idiocy of geo-restrictions. In my experience companies that fail to treat Canada and the US as a shared customer base fair poorly. They are much closer than they are different. It is not too difficult to consider Canada a location with slightly more interesting state and local law for US based customers.