[Iskariot]

If you read mostly and many PDF's and if they feature a lot of illustrations, graphics etc in color I would recommend thinking about a tablet.

Tablets also tend to have much more internal memory and because PDF's can be very large you might run out of internal memory in e-readers faster than you would like.

Of course the LCD displays of tablets are not as comfortable for reading as the e-ink displays.

If you insist on getting an e-reader I would start to first select devices based on size and work from there, because not many brands have 9" or larger models.

Pocketbook has some large screens. Perhaps they have what you need.