The Sony is good, but the technology is outdated (no wifi or 3g).
I have the iPad, which is a nice toy. As 4tees mentioned, it is really too heavy to hold comfortably for extended periods. It's strengths are its friendly interface, websurfing capability and suite of Apple-familiar application (i.e., ipod, mobile me, etc). I HATE that it does not have USB. I don't care about Flash. As an eReader, it's weight is a big negative. However, unlike e-ink technology, you can read in complete darkness because it is "self lighted". In fact, you have the option of changing the font to white text on a black background, which is very comfortable for night reading.
If I were to get an eReader for reading only, the Kindle would be my go-to unit. Light, great battery life and free 3g access (for downloading books and wikipedia). Hella cheaper than the iPad too.
btw, I use amazon/kindle for ebooks. Waaaaay better selection than ibooks.