Just depends on what's relevant to your interests. Some of the ones I'm subscribed to and read most frequently are r/TennesseePolitics, r/LowFantasyGaming, r/BlackMetal, r/PureASOIAF, r/pugs and, unfortunately, r/PetLoss at the moment. These are all relevant to my ongoing interests, but more importantly they're (almost) as specific as possible. When you narrow the scope (e.g. r/PureASOIAF instead of r/books or r/asoiaf), you tend to have better discussions and stricter moderation.