WB and BF

That is not something we can advise you on. Some prefer keeping many strong units for AA or for whatever reasons, some just want to max out their arena core as quick as possible.

But as to comparing Effie and Hardin, I personally thinks that Effie is more efficient than Hardin especially when she is merged up. Her atk comes in handy and is less reliant on special proc, not to mention her massive HP is really important against high power specials from sword units (which took down my +def, ward stacked hardin a few times).

Also, I asked this question once here and I have got replies favouring Hardin but in another day in a similar thread, many favours Effie instead. It really comes down to playstle and team needs at this point, so why not keep both first, and decide which one is better for your team later on?

Given that your Hardin is a -RES I am not sure I would go with a res stacking set for him. And like that Effie is pretty stiff competition. That said anytime you have to use A for DC instead of a breath the unit is at a disadvantage for that type of build. So Hardin should in theory be better than Effie in that defensive set up.

Of your bold options. . . Jeez. I would normally rate Zelgius the best but if you were running the standard Death Blow Brave Lance Effie I would vote her. Bonfire plus quickened pulse plus brave effect equates to some serious alpha strike damage. Works better on Jakob due to 2 range, but Effie smash could be lots of fun too. Thinking about it Black Luna is 3 as well. So Brave Sword Zelgius could blast off a black luna on the second Brave hit. . . that thought terrifies me. Too bad yours is -ATK. If I recall right that drops him out of the range I consider good fro braves.

Anyways I second just hanging onto him unless you feel really desperate for someone to have Bold Fighter.