I own a Kobo Touch and I love it. It is very simple to use and quite light. According to the Wiki article, it's 184g. It's very compact, which is a benefit of a touch screen - the bezel doesn't have to be as big. I like the feel of the finish as well.
The other nice thing about the Kobo is that it's more "open" than other readers, and it also has frequent firmware updates that add more features.
I also like that it tracks my reading - how many hours, pages, etc. For some reason I just find that a fun feature. It has wifi and a basic browser, but obviously the internet experience on an e-ink screen is so-so. Still, if you need it, it's there.
As far as your Kindle books, well, I've got bad news for you: Neither the Kobo or the Sony will read Kindle books, unless you convert them to Epub format. Neither will any other ereader. Kindle uses a proprietary format to prevent people from buying other devices.
The good news is that you can save your Kindle books. Calibre is a computer e-library program that can convert books from one format to another. You can download it here:
http://calibre-ebook.com/
However, it is likely that many of your Kindle books are DRM'ed, and this will prevent you from converting them. Google "apprentice alf." That's all I can tell you on the forums, but it will help you out with that.
...And all this trouble you'll have to go to in order to save your Kindle books is exactly why proprietary formats are bad. Your Kobo books will be readable on the Kobo (obviously) or the Sony, because they are the universal Epub format.