Who to refine?

The problem is that, as a guy who likes to make the best out of all my units, and recently I've had a dilemma between who to refine.

My options are my Seliph, +Res-Hp

Weapon is Tyrfing

Special is Bonfire

A Skill is Close Def3
B Slot is QR2
C Slot is still being worked on

Sacred Seal is either deflect melee or deflect magic.

Or

Ephraim,+Res-Def

Weapon is Siegmund

Special is Moonbow(Trying to get bonfire)

A skill is Close Def 3(Yeah, Joshua got sacrificed)
B Skill is Quick Riposte 3
C Skill and Sacred Seal are hone skills

Or Finally

Michalis Neutral IV's

Weapon is Hauteclere

Special is Aether

A Skill is Heavy Blade
B Skill is Quick Riposte 3
C Skill is Fortify Fliers
Sacred Seal is still up for grabs.

My Question is, would it be better to upgrade Tyrfing to Divine Tyrfing to make Seliph good at tanking, or would it be better to upgrade Siegmund to its +def versino and give my -def Ephraim the much needed upgrade he needs? Or would a better version of Michalis' Hauteclere me better for him?

Also any opinions on their builds would be nice. Thanks for the help!