I have two answers (Score 2, Informative)

I have used both. I also occasionally read books on my laptop. For most purposes, the eInk readers are a lot easier to read than LCD displays. I prefer the Sony Reader. DRM is not that much of an issue to me because I generally buy or download my books from non-Sony sources, BUT--and this is a major point--if you are a Mac User (or a Linux user), I recommend the Kindle. Sony, in their infinite ignorance, does not support anything but Windows. The other factor that I would check on is how many books are available in your format. I know a few people who have said that they couldn't find certain books for the Kindle that are available for the PRS-505. Personally, I have had the opposite results. One device that might bear watching is the OLPC computer because it offers the best of both worlds--it is a color display until you turn the brightness all the way down, and then it becomes a reflective gray scale display.