It depends on what it implies it being the only one on the bookshelf.

  Is it the one you consult often because it has so much timeless or deep knowledge?

  The one you loved the most so far and has a sentimental value?

  The one that is most impressive as a background in online meetings? :)

  The one you most want to read but haven't gotten around to yet?

I guess we'd get different and less conflicting answers here if everyone interpreted the question in the same manner.