Who should get Close Counter?

Jakob for sure. Henry doesn't quite have the defences to pull it off, and Jakob's A-skill is already a little lackluster anyways.

I feel you should give CC to Jakob because imho I feel he is the better unit. He has higher defense than Henry so he'll tank physical hits better. Also for your armor team you already have an armor march/green unit in Amelia which is kind of redundant since for me I prefer to make teams of each color for coverage and you only need 1 armor march unit. Slap on a brave bow and you have yourself a real monster. The only downside I can think of is that you lose out on magical damage, but that depends on you and your preferences.

I'm going to be the odd one out and say Henry and this is why: Gronnowl. With it he has excellent speed and he can make use of the new close defense seal to become incredibly tanky even on the physical side. You could also run Gronnblade with vantage, which will absolutely devastate most non-inflated units provided appropriate armor buffs (which aren't hard to come by). Meanwhile Jakob is rather meh and is better as a death blow brave bow build (it's what I did and he works great that way), and even more so for Henry because he's +atk!

If you have a spare Gronnowl+, Henry, if not, Jakob

If you have a Gronnowl+ to pair with Close Counter on H.Henry then him definitely.

If not then H.Jakob since he will do great using even his default weapon. Although adding a Slaying Bow+ or Brave Bow+ would make him even nuttier.