Well they are all wrong!
Just kidding.
The ereader you get depends on your opinions so check them all out. You want e-ink technology if what you want it for is only reading. But if you are going to get a new ereader, you want one that gives you options. I have a Sony PRS 505 and the wife has a 600. Please note, I am not specifically pushing Sony here but they are quite diverse and accept many formats. Granted 98% of what you might want to read will be in epub, but I have read PDF documents on the Sony and it worked great. I was quite please that Sony offered that as a compatible format.