I own a 7" tablet (Original samsung Galaxy Tab) and a 9.7" Tablet (HP Touchpad).
For reading books, the 7" form factor is vastly superior. Its right between the size of a hardback and a paperback. Its small enough to fit in your pocket and big enough to be wedged in crannies so that you can read 'hands free'.
The 9.7" tablets are too big to hold with one hand for a long time. They have twice the screen area which means you have more light straining your eyes and it is easier to lose your place on the page.
The smaller tablets are better for reading books in the same way that the larger tablets are better for web browsing.
That is my opinion, anyway.
For reading books, the 7" form factor is vastly superior. Its right between the size of a hardback and a paperback. Its small enough to fit in your pocket and big enough to be wedged in crannies so that you can read 'hands free'.
The 9.7" tablets are too big to hold with one hand for a long time. They have twice the screen area which means you have more light straining your eyes and it is easier to lose your place on the page.
The smaller tablets are better for reading books in the same way that the larger tablets are better for web browsing.
That is my opinion, anyway.