Much of the content of the History Channel is best likened to a comic book version of history. There is occasionally something worthwhile but most of it is just purile crap. The Military Channel is better, particularly with experts on stuff even if the occasional one is a bit strange.....
Discovery is good on some things, particularly shows were they are doing current stuff like How Its Made or Dirty Jobs (for which I still want to see poor Mike Rowe machine graphite for someone I know for a day....taking a bath after 8 hours of that makes the water grey. Even with a respirator you have black gunk in your nose. It is absolutely the nastiest job I've ever done....).