Personally think that it is fine to watch pronography with your partner but you shouldnt rely and addict on it too much. In terms of which category is not encourageable, I would say not to watch porno that involves underages (like what Pemikiran mentioned), animals or any illegal actions.
It depends on you and your partner decision in that matter. But if ok, not the type of underage, to discourage the making of underage porn. I think.