Personally I would go with Kindle.Here are Pros & Cons
Pros:
- Kindle is great for travel. It's wonderful to have a whole library at your fingertips in a slim, lightweight package.
- Download books on the fly. If you don't like what you're reading, just buy something new. Hear about an interesting book on a tv show or magazine? It can be yours in a minute.
- Easy to find and return to a specific topic, character or subject that you'd like to clarify or review later. No more thumbing through the book to find a passage.
- Kindle is a great conversation starter. People constantly ask what it is, how it works, etc. and are consistently amazed. Amazon should have a referral program...a free book for referring someone who buys a Kindle?
- The dictionary feature makes it easy to get the definition of an unfamiliar word.
- Great for reading in bed! You can keep your hands under the covers and still turn the pages, so your hands don't get cold. The Kindle is lighter and can be angled better in bed.
- The page forward and back buttons are conveniently and thoughtfully placed so that it's easy to change pages, while pages are not turned inadvertently.
- Long battery life if you turn off the wireless feature.
- Eliminates the problem of book storage. The books are always handy if you want to re-read them, but aren't cluttering up the house.

Cons:
- Charts, graphs, maps and photos are horrible. Even with the zoom feature, it is impossible to see detail.
- Still some glare when there is light behind you, but as I type this on my computer, I realize that my computer screen has much more glare.
- Crazy keyboard!
- Screen burn in is obvious at the bottom search area and along the margins of the screen, leaving ghosts of images.
- Not enough contrast.
- You can't share books with friends. So you have to buy books on Amazon.
- Many of his older titles are still not available on Kindle.
http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Fs%3Fie%3DUTF8%26ref%255F%3Dnb%255Fss%255Fkinh%255F3%255F6%26field-keywords%3Damazon%2520kindle%26url%3Dsearch-alias%253Delectronics%26sprefix%3Damazon&tag=computer0bd-20&linkCode=ur2&camp=1789&creative=390957

and for Sony
Pros:
- Fun and easy to use
- Its lightweight and you can hold a lot of books in the interior
- The e-ink technology is remarkable. Its a lot like reading a real book
- Fonts can be enlarged.
- The functionality of importing Word documents is excellent, particularly since almost anything online can be copied and pasted into Word. But the title of the documents isn't able to be changed and links to other places within the document don't work right

Cons :
- There's a large selection of books out there but not as large as you might want and sometimes the list doesn't always make sense.
- There's very little in the way of textbooks, professional or academic.
- The ability to read PDFs is a good thing, but you can't read the actual contents because you can't zoom on them. So, it can be a useful for storage but not so much for reading.
- You can have hundreds of books on the Reader. But you can only read one at any given moment.
http://www.amazon.com/gp/redirect.html?ie=UTF8&location=http%3A%2F%2Fwww.amazon.com%2Fs%3Fie%3DUTF8%26ref%255F%3Dnb%255Fss%255Fe%26field-keywords%3DSony%2520Reader%2520Digital%2520Book%26url%3Dsearch-alias%253Delectronics&tag=computer0bd-20&linkCode=ur2&camp=1789&creative=390957