I have both also. I prefer the Kindle (for one, the screen attracts MUCH less dust than the Sony for some reason) and the Internet to get books (i.e. Feedbooks) is cool.
However the Sony has one big pro: Adobe Digital Editions (ADE). I can download books from my library and read them for 21 days each. They also have PRC for the Kindle but there are TONS more ADE books (and more ADE books get added than PRC and that trend will continue... out of the most recent 200 books added to my library, only ONE was in dual-format (there are no books that are only in PRC format, they are either in both formats or ADE only).
The Kindle gets that, the Sony gets stowed away in the closet. I love my Kindle
