With posts, I mostly skim the titles for what looks interesting. I take fewer comments as a bonus but I can't say exactly why (less noise?). I don't look at the votes (though it obviously contributes to what I see).

With books, I mostly read based on individual recommendations (or references). It's more natural to me than going with what's popular though it doesn't exclude it. It has the bonus of being an imperfect quality filter which mixes the good (as determined by people I trust) with the unusual.

To be honest, when I have read books based specifically on popularity I've been thoroughly disappointed. Reading Thinking Fast and Slow was mostly challenging with a mixture of bad examples and bad terminology ("systems 1 and 2"). I enjoyed the book a whole lot more near the end when it was discussing the incompleteness of/problems with economics. Some of my distaste for the earlier parts possibly comes from exposure to critics beforehand (e.g. Gerd Gigerenzer) and to the optical illusions. Similarly Surely You're Joking, Mr Feynman! can be amusing but a lot of the stories boil down to "aren't I clever?".