Dedicated e-ink device or mobile app?
I've had a kindle Paperwhite for about 3 years. I use it for one thing, which is reading through my massive amount of pirated Discworld/Haruki Murakami books while traveling. All I want it to be able to do is carry a shit ton of books, and allow me to read them for a long time. The e-ink display is very visible and its low energy impact lets me use it for a ton of time. I like it a lot for this specific task.
I think the problem that I will always have with Kindles (or any e-reader, for that matter), is that there is no good way for me to share a copy - specifically, my copy - of a well loved book with a friend. Reading is and has always been a largely social activity for me, in that I get more joy out of discussing a book with a friend who has read it than simply reading it on my own. I love sharing an unknown book with a friend, especially if they really enjoy it. E-readers tend to actively discourage that, if not sterilize the process.
I like having to explain why my copy of Invisible Cities has bite marks on it, or talking about which short stories I have dog-eared in Palm of the Hand Stories. My copy of Emerson's collected works is at least 50% underlined/highlighted at this point, and I wouldn't want to read it any other way.
I think that there is so much about e-readers that is better - on paper, at least. If I viewed reading as a more isolated activity, I think I would like it more.