I got into Sony ereaders late in the game, with a T1, and really enjoyed it for reading.

Unfortunately, I also enjoy modifying the software on my devices. On that front, I found the T1 exceedingly fragile and I ended up breaking it. I think, in the future, I'll stick to Kobo devices since they are much friendlier on that front.

muse: I was under the impression that unlocking the bootloader was vendor dependent. If you do you research and find a vendor that ships with an unlocked bootloader or provides a service to unlock your bootloader, you're in good shape. Since there is a multitude of Android devices out there, it's also a good idea to verify that there is a working recovery and firmware before making the purchase. (For most popular devices, there will be. For the less popular devices, you'll either have to spend a great deal of time developing your own solution or have to deal with potential bugs.)