While I did not check out the Sony, I seriously LOVE my Kindle, I looked at a few and wrote a
review about it here.
What I think is the biggest benefit to the Kindle is the access to books at Amazon. Amazon is a HUGE online retailer and is not going away anytime soon. It is super simple to get books, etc. This is just my personal opinion. I don't regret my decision and I have the older version of the Kindle which was over $200. The latest Kindle is under $200 and probably has made improvements!
Also, as far as customer service, Amazon was great. I dropped my Kindle (only a couple feet) and the screen got messed up. I called them and since it was within a year, they overnighted me a new one (in one day) with a box to return my old one - EASY! So, there you go!