List of good candidates for Close counter?

Of units that come in the regular pool, Leon gets my vote for CC archer. He has the Defense to duel melee units, is easily available (for good IV's and merges), and his base kit is pretty good as it is. I also think Boey is in a similar situation with good Defense and access to Gronnowl which is pretty defense-based.

Personally only range armored units can use the skill well(well it's kinda mde for them at this point in the game)

but units in the normal summoning pool like Leon, Nino(weird yes but I saw it and it works) basically any unit that has good bulk on obth physical and magic sides.

From the base set Boey and Sophia can use CC best.
Sophia however is in my opinion slightly better, because she has great mixed defenses so she can even tank common dragons (Myrrh, M!Grima, A!Tiki). Also it's pretty likely that she gets a refinement (Apocalypse).
However the without a doubt best users for CC are armored mages, so I would just wait till you get one of those.

Oliver. hear me out here. this isn't really an amazing build but its funny as all hell and makes Oliver a viable unit sort of. build this only if you really want to:
W: Blarowl (+def)
Sup: Swap
Spec: Iceburge
A: Close Counter
B: Quick Reposte 3 (or 2 if you must)
C: Atk Ploy 3 (or any other ploy skill)
S: Fortress Def 3
he ends off with 42 health, 40 atk, 20 spd, 31 def, and 34 res. generally good stat spread as well as solid mix bulk. This is more or less just for fun don't expect it to be amazing or whatever. otherwise just wait for H Henry or H Jakob. Or you can try another dumb build with l'arachel:
IV (+def, -hp)
W: Blarowl (+def)
Sup: reposition
Spec: iceberge
A:Close Counter
B: Quick Reposte 3 (or 2)
C: Atk Ploy 3 (again or any ploy)
S: Close Def 3
she ends with 30 hp, 44 atk, 31 spd, 23 def, 31 res, and an effective 29 def and 37 res against 1 range enemies. Once again just for fun and don't do it unless you really REALLY want to. much worse than oliver but much more funny.