I've owned ebook readers by Amazon, Sony and Kobo. The Kobo Aura HD is imo the best for reading (unless the field has changed in the last year). For 3 reasons:
1. Bigger screen than the standard Kindle (there was the DX, but not sure if it's still in production, and if it is, it's bloody huge)
2. Choice of fonts. For some reason, this does make a difference to me and I use different fonts for different books. I know this doesn't seem to make a whole lot of sense, but I notice it.
3. The HD now comes in a waterproof version. Which is incredibly cool- you can use it in the bathtub or by a pool.
For academic papers, if you are reading PDF, ebook readers suck though. The screens are too small (the DX was regarded as okay) and don't update quickly enough to scroll around on when zoomed into a PDF page. If you're reading a proper ebook file, they are fine. But you can't easily annotate if that's what you need to do. I imagine annotating on a tablet is much easier.
I also have an iPad and a Mini. I don't use either for reading anything beyond online news articles. Tablets suck ass for extended reading sessions.