The bigger one would be better for technical books, but I'd prefer the small one for regular books. By clunky, I almost mean it literally. The little joystick thing is small and awkward to use - you move the cursor around the screen one step at a time, and there's a very slight, very annoying delay between input and action. It's begging for a touch screen and color. The keyboard is small, and probably slightly less usable than the ipad keyboard. Flipping pages is also strange, in that there are dedicated buttons, but I keep finding myself clicking the wrong one. That would probably go away over time, but it's annoying, and I did not have that problem with the iPad, which is very intuitive.
Given the price difference between the big Kindle and the cheapest iPad, I'd probably go with the iPad unless money is a huge factor. The keyboard is nicer, the touch screen is a huge benefit for things like using the dictionary, table of contents and bookmarks. Flipping pages is more intuitive. Install the Kindle app and iBook, and you're good to go. The only caveat to this would be if you really like the kindle display. It is different, and I can image some people putting up with the Kindle's lack of polish to have the screen. I wouldn't call it better, but it is different.