I agree with those who say you can't just line up the specs and do the arithmetic to determine the best device. There are too many factors that are specific to the individual's needs and his or her purpose for buying the device.
For example, I bought a Nexus 7 to give to my husband as a birthday present. My primary reason for getting it was to share my e-books with him. However, I could not stand reading on it AT ALL. Not even for a couple of pages. I tinkered with all of the options and could not get to a comfortable view. Knowing my husband's eyes are even more sensitive than mine, I took it back (and got him a PlayStation, lol).
It would be easy to say, "Well, you just don't like reading on a backlit screen." And that's true - to a point. However, I did find a backlit screen that I can read quite comfortably - my Samsung Galaxy S II (Epic Touch 4G blah blah blah) phone. This leads me to believe that it's the area of the backlit screen that makes the difference for me - there's only so much I can take, but below that threshold, I enjoy using the device to read.
My point is, each person has his or her own little quirks that create an unknown variable when determining the "best" device.