I think Shield Braker, as far as I know Guard Break applies to melee only, you can still miss physical skills after using Guard Breaker. Someone who melees bosses may appreciate Guard Break though, however, I never tested or saw someone using this combination myself.
For your Bunny, Shield Breaker is the skill that you should get, as Guard Break from the guardian will simply displace yours.
Recette - Witch 400 | EmiriTachibana - Diva 400 | SakuraHiiragi - Champion 35x | AnaJessicaAyano - Soul Master 26x | LeslieSun - Witch 26x
Bye Bright Shadow Japan, I will miss you all and my bunch of characters very much ~~