Who are the top users of DC?

Pretty much any armor unit who isn't named The Black Knight or Zelgius. Joshua is also good because of his weapon increasing his Res, making him a natural mage counter. Some people say Ayra, but her Res isn't really high enough for it in my opinion. A pretty good one I've seen is Eirika. Her defenses are good on both counts, and her speed quite high. Had a few unpleasant surprises from that in the arena.

Effie and Winter Chrom become gods with DC. just make sure to give him/her hone attack 1 so you can also inherit goad armour at the same time.

Effie with Berkut's Lance and the DD seal is a very good combo

I think Sigurd is the best user of DC in the game. Else, Armor heros and Mia/Ayra are great user of DC.

Technically an armor unit like Lissa or Sheena or winter robin will want it the most. Or you could throw it on someone like Lloyd or Mathilda and make a gimmick mage tank (there’s a wrath build for distant counter Hawkeye that destroys Mages in one hit on this site)

But back on topic of like, actual viable practical build: I’ve seen Arya use it and basically become Better Ryoma™️, for armor emblem it helps Sheena a lot.

Sadly you’ll mostly be focusing on units with good res to use distant counter because dagger units are... dagger units. And archers are either a brave bow desperation build on someone like bridelia or its Brave Lyn who ignores distant counter entirely. Mixed tanks can fight regular archers well, again that’s where you can see Sheena or really anyone with good def and res like maybe Selena or Camilla or saber. I know people give it to Effie a lot and give her Berkut’s lance, I personally don’t see the appeal but I don’t un armor emblem or Effie in general so I can’t give my opinion on that too much but yeah that’s definitely a viable build