I own both K1 and K2. K2 is my daily reader and K1 is my back-up and really the holder of all my ebooks. K1 is my library. Like rcuardo, I find the ergonomics of K1 to be better because of the thickness and shape but navigation on K2 is faster and easier (though I do miss the little silver cursor
).
Should I buy a future Kindle, K2 will be the one to go up for sale on eBay. I'll never sell K1 because I'm so attached to it.