HN by far. Facebook doesn't offer me anything interesting except the convenience of not having people ask "when are you going to get a Facebook account?" (answer, 2004 when it didn't suck).
I check HN at least twice a day. I find myself going nearly a week between Facebook visits now. Many of my friends the same. I don't want to delete my FB, but I feel like it's becoming less and less relevant.
FB about once a semester. I already spend too much time on more worthy information to even remember it exists. Its emails are automatically moved to a maildir folder that i tend to ignore.
I just use FB for sharing photos with close friends and family and keeping (passively) in touch with others.