The 902 is the model without the digitizer; 903 has an inductive digitizer (i.e. stylus only). Sadly, there's no firmware thus far that lets you handily take notes on PDFs, barring
review's hack. A beta firmware has it for FBreader, so it may be in the works, but who knows how long.
Boox has
at least some freehand note taking, and they've demonstrated
selection zoom (an inexplicable omission on the Pocketbook).
Scanned images are typically not a problem for the viewers; when paging forwards, they may even prerender a page while you read the one before. Some complex PDFs get heavy, but it's not really dependent on size the way many assume. I've had some
extreme results involving nearly a minute for a page turn, but at least I could choose another viewer that didn't have the problem.
At a quick glance, I'd lean towards the M90, but this is from single-sided experience. It's sad that I only reach recommending against what I have experience with.