Having used a Kindle, albeit for a short time, an iPad, iPhone and any number of LCD's and since we are talking about reading, then I would say that the e-ink screen kills the LCD and from everything I have read (sorry no references to back this up) I gather that the general belief follows my "Opinion", for what it's worth.
In fact I find the iPad/iPhone the hardest one to read of the bunch, I find I can only stand to read for a couple of hours (I do a lot of reading at work). The iPhone is just too small for my eyes. Its not that the iPad is too bright, I don't know how to describe it, but too sharp? I can't think of another way to say it.
Because I work in Graphic arts, my days are spent in front of one type of screen or other. In the old days when we were still doing page layout on mono screens, we thought we had died and gone to heaven when we got a paper white portrait monitor (SONY, if I remember right, 25 years ago) to do the typesetting.
I found the Kindle to be closest to reading a paper book compared to the LCD, but does this mean everyone will also, I doubt it but you didn't ask for scientific reasoning, just an opinion.
"Opinions and a$$holes, everyones got one"