Nexus 7, Original Nook, and Kindle Touch
I bought the original Nook ($35), and the first Kindle Touch ($41) on eBay so that I can put drafts of my book on them, then lend them to friends or family for proofreading.
So, from the perspective of someone who has all three ...
The e-ink for the e-readers is surprisingly nice. I prefer it to my normal-display Nexus 7. There's something pleasing about it--I guess it feels more like a real book.
And, reading outside in direct sunlight is a pleasure.
Although the interface on the Nook is klunky, for just reading, I prefer it to the Kindle. Perhaps it's because it came with a super-nice leather cover, or because I can advance the pages by squeezing the bezel rather than by tapping the screen.
Reading on the Nexus is still good, and it's convenient to be able to use it in the dark, but there's something nice about the e-ink readers.