Wikipedia has a number of pages dedicated to this sort of thing; http://en.wikipedia.org/wiki/Comparison_of_e-book_readers
I personally have the pocketbook 301+. I've had it for over a year now and love it. At the time I got it, it had the fastest refresh rate of any of the e-ink displays on the market, which was a huge draw. It supports many formats, with some hope of adding more support. It's pretty much a barebones ereader. it does one thing well. There is no wifi or touchscreen or any of that. The battery last a good long time, I often go weeks with out charging it, occasionally months if school has been particularly busy (no time for pleasure reading).
I've been interested in tablets as reading devices but get turned off by the price and the fact that I don't much care for extended reading on light emitting displays. Truth be told, i don't know nearly enough about tablets and their battery life, displays, support, to offer an opinion here. If anyone with some experience could chime in?