I'd vote for Sony. My thoughts were in this thread. To that I'd add that I think the Sony has a much more lovely 'feel' to it, DH's Kindle feels kind of plasticky to me and the keyboard just seems so utterly pointless and 'cluttery' - my Sony is all sleek and shiny. Also you don't get the annoying screen saver (can be disabled on the Sony, Amazon are planning an 'ad supported' version of the Kindle in the future I believe so you can't disable the screen saver without jailbreaking it).
The advantage the Kindle has is that some covers run the light off the Kindle power so you don't have to worry about batteries, however I've just got a clip on light that goes on my cover.
I have a Kindle and I love it. I am still trying to get over the fact that it just doesn't look like a screen- It looks like a page! Also, lots of books free to download off amazon, and it's just so easy. And I adore the screensavers. No experience of the e-reader, though.
I have a colleague with a Kindle and a colleague with a Sony Reader, and I borrowed both devices one lunchtime to have a play do some research.
"Page" turning - this was faster on the Kindle than the Sony - in fact on the Sony, I found it slow enough to interrupt my "train of reading" Typeface size - more options on the Kindle (important if you have just started needing glasses to read - I can make the type size large enough on the Kindle to read without glasses Weight - the Sony was lighter than the Kindle (both in covers)
Both were easy to use and fairly intuitive.
On the basis of this very interesting lunchtime and fairly limited research, I decided that I preferred the Kindle, and, six months later, am the proud owner of one. I've had it for a month and am very pleased with it
I have a Kindle, an Iphone and an Ipad, and love the syncing thing. You just need the Kindle apps on the Ipad and Iphone, log in with your kindle account details and then it syncs the page whenever you open the app, so long as your devices are all connected to Wifi or 3G (you can turn it off on the Kindle to save the batteries).