Originally Posted by nairbv
Since I'm not willing to pay for terrible DRM, and no decent DRM exists, there's no sense basing my purchasing decision on what DRM format is supported.
Then I am not sure why you are leaving the Sony off of your list. You don't have to buy books from the Sony store. I haven't yet. The Sony supports HTML, Txt, RTF, PDF (correctly formated) and the LRF format without DRM.
However, it seems at this point that DRM is going to be something you might have to deal with if you want to buy mainstream books. As you said, in this case Mobi "seems" to be the most portable. Although it is my understanding you still need to get the file for the correct PIDs. I'm not sure if the stores allow you to go back and change your PID and redownload. That seems like an invitation to piracy.