Thanks for the response. I am planning to read mostly scientific pdfs, so usually 2-3 columns and 0-2 figures per page. I have seen that the paperwhite has ok annotations and a nice
zoom to column feature (seems to also be
available in KOreader).
I am planning to buy books, sideload PDFs (sometimes from textbooks), and download free books from project gutenberg and similar sites.
To rephrase my questions around open source: Has any of these companies showed a history of supporting open source software or open standards for ereaders (for example by releasing the code to their own software)? If so, I would like to support that company if the products are somewhat similar in terms of features and price.