From what I read and experianced actually using all the ereaders (Kindle, Nook and Sony)… I would put the kindle last. The kindle is the fastest of the 3 but it basically ends there. The added features sony and the nook have trump the kindle IMHO (but everyone feels differently) The Sony has access to more free books then the kindle or the nook. The nook software allows you to share books for 15 days at a time and if you like going to the barnes and noble store you can read their e-books for free while in the store to know if you want to buy.
Personally, I ended up with an Ipad and love it. The I-pad with IAnnotate is the best PDF reader, highlighter and modifier out there. I got it just for this feature to make my conducting my literature review a lot easier.
If you have some specific questions let me know. [/quote]
You can also rent books for free from your library through the Sony.
I have a kindle and like it, but there are some things I prefer in the other ones.