What about the 75 dollar credit?
I managed to drop my Sony 700 enough times to brick it. Nothing I tried to reset it would work. However, I went to the Sony Style Store online and read about the $75 credit offer. They will take back units, working or not, and give you up to a $75 credit, so I answered the brief questions asked on the site and then printed out a shipping label and shipped my machine back to them. In a few days I had my $75 credit and bought a Sony 950. If price really is the determining factor for you, look into the $75 credit.
I could have gotten a 650 but with the discount I decided I wanted the larger screen. Dictionaries come with both the 650 and 950, so that was neutral to the decision. You can take typed or handwritten notes on the Sony, which is both fun and useful. The touch screen means you can turn a page by swiping the screen anywhere not just where the buttons are and no, you can't see smudges because the screen is not shiny like an iPhone.
My wife has the K3, but I'm not into best sellers and I'd rather browse booksellers on a real computer with a big screen. Also, I'd tried reading a pdf on her machine and unfortunately pdf's don't render as well as they do on the Sony, and at least the ones I tried, I couldn't change the font, whereas with the Sony text reflowed pdf's you can change font size. I don't care about wifi or 3G, for the reasons others have mentioned, but my wife loves it, because she doesn't have to fire up the pc to order more books, so consider that.
Hope this helps, whatever you decide, you've already made the best choice by chosing ereading over paper books or a tablet, or some dinky phone screen.