Having an integrable folio-style keyboard is a hard requirement, and Apple seem to be filling this niche, though their manufacturer (Logitech) is the same company I've had an horrible experience with myself.
at 9", almost all PDF-format texts are readable, though good bookreading software is hard to come by. I've mostly settled on PocketBook, which is reasonably inobtrusive for reading, but which makes large-scale document management (10k+ items) impossible. The metadata fields, as an example, lack an author field, and updating content metadata is cumbersome to the point of being all but impossible.
I've been hunting for alternatives, but to date, no joy. Apple's devices look superior based on hardware, though I have concerns for the actual usage experience.
I have no use for writing in a tablet. Can anyone recommend a big e-reader suitable for textbooks? I'd like a 13" Kindle or something...