We only have the Sony e-reader, so can only give opinion on that. It is an easy tool to use, and the screen is clear and easy to read. There is no backlight, but we have a case with a built in light in case you fancy reading it in the dark
It charges over USB, or if you have a PSP you can use the power supply from that to also charge (much more efficient!!). It supports PDF's and word documents, and you can see images in greyscale (obviously).
As nice as it is though, I just like having real books

This is handy for when you are going away for a few weeks, or for commuting (or showing off!!) but at home for me a real book can't be beaten
Shaz