[anigbrowl]

Well, I should have said the overriding factor, but my reasoning is that a lot of what appears to be 'popularity' is just the result of marketing campaigns by publishers, as opposed to the sort of enduring popularity that comes from being loved by readers (which can't be determined until some time after a book's release).

That said, I would still prioritize variety over pure popularity. For example, I can see a library having 2 or 3 copies of all the Harry Potter books because people keep checking them out, but I don't think they need 10 copies.

[jubilanti]

And your sense of what books are truly quality is in no way impacted by "marketing" to you? Let me guess, are you one of those people who thinks that ads work on other people, but not them?

Your idea of what makes a book good or bad is as much influenced by the marketing you are exposed to. You're just subjected to a different kind of marketing than the general public.