Kindle Paperwhite and Kindle Keyboard 3G.
To keep things simple, I'll review the paperwhite by comparing it to the 3G. I used the 3G as my e-reader for about two years before I got the paperwhite this past Christmas.
Pros: It's awesome for reading at night. Easily the most nonintrusive way to read in the dark that I've ever come across. It's far better for your significant other than having the lamp on or using a full blown tablet. With the backlight low, it's very easy on your eyes too.
Cons: It's battery life is significantly shorter than the older versions of the Kindle, be they the Keyboard 3G or any of the others. Whereas I could use the Kindle 3G for two weeks plus without recharging, the paperwhite can only go about a week, assuming you're using it heavily and steady, before requiring a plug in. My 3G plus has become my go-to travel reader for exactly this reason.
Personal issue: I'm a scribbler and marker. I extremely dislike the touchscreen highlight feature on the Kindle Paperwhite, and I absolutely hate the highlight feature on the Keyboard 3G. I would much rather be able to write in the margins. I know this probably just something I'm going to have to get use to, but jesus, I've been scribbling since I was 12, it's hard to just give that up.