Earlier quoted context omitted.
I started out by reading the sites directly, but the comments here are so good that I frequently go to the comments first and read them. I also tend to not read stories that have been upvoted but received no comments.
Those are often the most though-provoking ones.
That is not what I would call "thought-provoking" its a post of limited scope which, while it may be interesting to someone who knows about the topic, does not leave much to be discussed.
It is the discussions that bring me to HN and keep me coming back. I frequently don't even read the articles, because I find the commenters here are of a much closer mind-set to myself, and often know as much or more about the subject than the blogger making the post. A heavily commented article is one I am most likely to read, because it means there is likely something I can add to the conversation.