So far the best PDF annotation device, I have used is the Surface Pro 3. At 12 inches it displays PDFs very well. The pen is pressure sensitive and will reject any outside inputs.
The only feature I would want integrated is the "infinite workspace" of papyrus. But even then who cares I can still have infinite pages.
Thanks
I think you can import PDF's into Lecture Notes also, and annotate around them there, but I haven't bothered trying that, and I /expect/ it'd feel sluggish.