single book, search results

The other question whether we should prefer web or print ISBN is IMO much more complex.
<blockquote>but Web and Print do not [...] refer to the same exact item</blockquote>
This statement very much depends to what level</a> you are looking at: <a href="https://en.wikipedia.org/wiki/Functional_Requirements_for_Bibliographic_Records">work - expression - manifestation - item</a>. Moreover, this can make a difference in citations: line 3, page 48 in the kindle edition of a book is maybe different from the same reference of the print book. However, this might be more philosophical questions...

Personally, I would prefer the print ISBN, because that is much more used than the web isbn (which might even be different on a different plattform), i.e. the results for any catalogue or bookshop is IMO better with print ISBN.