If you keep the Kindle you could transfer all of your epub files from the Sony without having to convert. Also, I've found that some Canadian titles are first published as epubs, and then at the Kindle store; in fact, there were some titles that I could only find as epub. They may have later been made available at the Kindle store, I don't know.
Then again, some people have found titles at the Kindle store which were not available in epub format, so ymmv.
I personally like using a touch screen, and the Kobo allows you to simply tap to turn a page, you don't have to swipe.
Personally? I'd probably keep both devices. That way, you get the best of both worlds.
I know, I'm terrible!