For me it comes down to what sort of book is in question and how long I want to keep it:
- Books that are graphic heavy, especially color graphics, or contain a lot of tables and formulas.
- If I only want it short term I will get it in paper from the library.
- If I want it in my permanent library I will buy it in paper.
- Books that are straight text or only B&W graphics.
- If it is available in ebook format in public domain I'll get that obviously.
- If I want a permanent copy, it is available in ebook format, at a cost I will buy the ebook format and strip the DRM so I will always be able to view it now and in the future.
- If I don't want a permanent copy and it is in ebook format from my library I will get it there.
- If it is not available from my library as an ebook I will get from the library in paper.
So I guess the bottom line is the only paper books I will buy are books with color graphics that I want to own permanently. Other then that my choice is an ebook.