I dont understand why you think ipad is the best
it's screen characteristics are convenient to display an A4 pdf?
it is because of better image clarity, or color representation, or wide viewing angles in ipad?
because, imo, the best thing for that kind of use, it's not to have to scroll to see the full page and not to have to magnify in order to see the text
so, you suggest ipad, for its advantage on that?