The Kobo can run in a fully offline mode (called "side-load mode" or something like that) and I can transfer my ebooks directly via USB. I use the Kobo most of the time now since most of my reading lately has been independently published ebooks, but I still use the Kindle for books I purchase via Amazon directly.
With all that said, I personally think the Kindle Paperwhite is already the perfect size. It fits snuggly in my back pocket and strikes the perfect balance between screen size being large, but not too large to hold for my average male hands. I'd be a bit concerned about the size increase for my personal use case, but Amazon does a great job with the Kindle in general so I'd like to see some reviews.
As for the new Colorsoft, I'd really like to see some reviews. The color Kobos that came out earlier this year got some mixed reviews for colors, but I'm not sure if that's just the nature of color e-ink or not.