To be fair you're currently watching a lot of interesting dramas!
If it were me I'd prioritise The King of Pigs, mainly because I watched it quite recently and found it very impactful. Or possibly Stranger 1/2, as I'm planning to watch them myself before Dong Jae: The Good or the Bastard starts airing.
Or The Guest, Connection, Missing: The Other Side S2, The Kidnapping Day...you've got so, so many k-dramas on your currently watching list I loved and would recommend watching! Perhaps a poll might be a plan ^^