At its best HN is critical and discerning, which are necessary qualities for raising the discourse to a higher intellectual plane (otherwise this would just be Reddit). At its worst it is cynical and contrarian. Those are flip sides of the same coin.
HN is like UChicago. Cerebral, academic, rigorous and always ready to shoot down sloppy thinking.
Quora is more like Northwestern. Intelligent, emotionally savvy, and projects a sense of polish.