I have both the
Cybook and the
BeBook. I purchased the Cybook when it was the only one which supported Mobipocket. Now that BeBook supports Mobipocket it is the one I recommend to everyone. It's a solid reader and easy to use. I found the default firmware very usable and think it would be sufficient for most people.
If you are interested in further customizing your reading experience I second Clee's recommendation for
OpenInkpot. The people working on OI have put in a lot of time and effort to create a very slick firmware for the Hanlin family of eBook Readers.