I'll throw my opinion in since I've owned a lot of ereaders
-Kindle Fire : nice size, a little heavier (vs regular Kindle) for extended reading. I sold mine because it did not do so well as a back up web browser.
-Kindle Keyboard : Probably my favorite eInk reader. Light efficient no problems with this one ever (I sold mine when I upgraded to the Fire)
-Kindle Paperwhite : was my primary reader (until I bought this mini) the lighting system wasn't perfect, but its better than an external light. Good if you do lots of reading in he dark in bed.
iPad mini : the perfect mix IMO of weight size and functionality if you're using it as your main reader. It's light enough for extended one handed reading. The other stuff apps/browsing/email are flawless Apple. text isn't pixelated unless you read in giant text/blind mode. Only knock so far on it as a reader is that the side bezel is thin, so there's a lot of accidental page turns.