Brave Ike or Amelia for DC?

Do not give distant counter to anyone. In my opinion, you should keep both hectors and put them on your defensive team. If your hector has a bad IV set though, you can give it to amelia and make her a "second Hector." Amelia basically has no weaknesses, so increasing her survivability would be a great idea. Keep ike with steady breath because that makes Aether proc really quickly, meaning he can dish out massive damage almost every turn.

Do not give distant counter to anyone. In my opinion, you should keep both hectors and put them on your defensive team. If your hector has a bad IV set though, you can give it to amelia and make her a "second Hector." Amelia basically has no weaknesses, so increasing her survivability would be a great idea. Keep ike with steady breath because that makes Aether proc really quickly, meaning he can dish out massive damage almost every turn.

Distant counter is very valuable so you could afford to hand one down to someone else rather than just keeping two Hector's, using two Hectors for arena defense is not recommended as it's easy to get around him. Other units benefit from this greatly so feed off the bad Hector to someone else for this skill.

Distant Counter is good for armor units like Zephiel or for units who can dish a lot of damage to mages while still suppressing their incoming attack.

Amelia's C passive for her in particular gives her a litttle bit of a break with not having to bait nearly as much as Hector would. She has the mobility to catch mages quicker and take them out unlike Zephiel, Effie, or Hector, and it frees her A passive for something better.

Don't get me wrong, she would be a great candidate, but she's pretty powerful without it.

I think Ike would be better suited due to his massive attack and potential to mitigate consecutive damage. I don't know the numbers at all, but 80% reduction and his color advantage will help him stop blue mages better than most units I would think. Like I said, I don't know the numbers in term of damage, but yea.

I would totally agree with Zephiel. I'm at the same point at wondering if I should give him DC but I decided to wait for the Black Knight that might be the best red armor unit when he's out. If you plan to give it to Brave Ike let me notice that his Weapon effect with the damage reduction only applies when he's attacked 2 times immediately after another. DC would let him counter attack after taking the first hit of a mage. So there is no 80% reduction when he takes the second hit if he doesn't kill the enemy with his counter hit. When you are cool with giving away his weapon effect then he has a good DC+QR build (Reinhardts Daring Thunder is reduced anyway due to being a brave weapon). But both Amelia and Ike are still very good without DC so I would suggest waiting for another unit that really benefit from it.