OP here. I finally added 4chan's /r9k/ and /pol/ to my blocklist since I often whined about them and yet I kept visiting them. While there are a few good posts and threads once in a while, most of them are trash and full with bots. /a/ is from the few 4chan boards that are barely passable and I can find lots of good material there. same goes for /d/ and /trash/.