I've owned a few Sony eInk readers in the past, but for my eyes, I never liked the low contrast. In recent years, I've been reading on either my phone or tablet.
Recently, when Radio Shack was blowing out those Nook Simple Touch readers for $20, I thought I'd get one to see if the eInk screens has improved. Although the Simple Touch is a very nice reader, it doesn't appear to me that the screen contrast is any better than the last Sony Reader I had. I didn't feel too bad, having only spent $20. I gave the Nook to a friend and he thinks it's great.
After reading reviews for both the Simple Touch w/Glowlight and the Kindle Paperwhite, it seems that the Paperwhite takes the prize for screen readability. So, I headed up to Best Buy and joined the Dark Side
I have all along resisted joining the Kindle ecosystem, preferring to stay with epub. I have taken advantage of the Kindle freebies, however. I have both Aldiko and Kindle apps on my phone and tablet.
Even with all of my reservations about ebook formats, I will say that the Paperwhite is the best eInk reader I've ever seen. With the front light adjusted to suit the ambient conditions, I find the Paperwhite very readable, and the matt screen isn't as reflective as my phone or tablet.
I still prefer epub and will purchase that format when I need to buy. I have found that dropping an epub onto the command-line tool kindlegen produces a Kindle ebook that is essentially the same format as the original epub. It is an extra step to convert, but is not too big a nuisance.
So, although I really like the Paperwhite, I will still resist going completely over to the Dark Side by not purchasing Kindle books. And I have recently learned that the latest Kindle book format is just a binary conversion of an epub. So, even though Amazon is embracing epub as a better format, they continue to make it proprietary.
Joe