I'm playing jade and mid-token dru, murloc paladin at moment, so any of this card can improve my decks. But actually I prefer more controlish gamestyle and also like mage and warlock very much, but they are not so competitive at moment :( I have nearly all playable legs from classic, and according to DK have druid, paladin and warlock.
So about the choices, I have feeling that Black Knight can be the most universal choice for current meta, but huh I already crafted and dusted him twice long time ago :D Should I do that again?
Finja looks like staple in muloc-pal, but well, I have seen that somebody played it against me just 1 or 2 times last season. Also I did 65% winrate on my road to legend without him last season... Maybe it is not so required for paladin actually?
Kun looks like really great tempo swing card for dru, but what if ramp will be nerfed? Or maybe Black Knight is better addition for druid anyway?
Or maybe it is better not to spend dust and wait for upcoming druid nerf and then look at meta? Maybe that will be a time to craft Mage DK?
I'd say Kun because I like it, but it isn't an easy decision, indeed. Kun and Finja will rotate out next year so keep in mind this in your crafting. The Black Knight Maybe it's the right decision but just because people are playing taunt warriors again.