SE is much more difficult to start using than Quora, which is also probably why it has higher quality content. Quora has absolutely no quality control.
That's definitely true, though I find that the less technical platforms are laxer. However, that level of quality control is exactly what keeps me coming back. If you ask a stupid question, SO is going point it out rather bluntly. Quora will give you a best-effort answer so someone can plug their latest product.
Ask a vague question on Quora, and you'll get a vague answer.
Ask a vague question on Stack Overflow, and you'll get downvoted along with comments to the order of, "You haven't provided enough information for us to give you an answer."
quora did SEO right. It has huge visibility, and thus, high quality answers get huge votes, even from people who aren't from that field of expertise. So perhaps post quality is lower than SE, but vote quality is magnitudes higher in my experience.
Maybe I'm misunderstanding you, but I've looked things up on Google and frequently see Quora answers at the very top.
I'd say at least half the time I click on the link, the top answer, it is either highly biased, anecdotal, just plain wrong, or a combination of those things. Many of the answers are also in broken English. Despite this, the answers get thousands of upvotes and it makes me question whether or not the Quora userbase is competent at identifying good content.
Over time, I've grown to not trust the first answer on Quora as I trust the top answer on SE. At that point, the Quora result becomes a waste of an entry on Google's front page.
As others have said in this thread, Quora seems to be suited towards personal questions and opinion-based questions, in which case, maybe Quora and SE are compliments to each other.
