The following macro will cast whom you have selected Blessing of Might if the person is either a Rogue or a Warrior and Blessing of Wisdom for everybody else.
/script class = UnitClass("target"); if ((class=="Rogue") or (class=="Warrior")) then CastSpellByName("Blessing of Might()");else CastSpellByName("Blessing of Wisdom()");end
add Hunter to the BoM classes
We love that blessing 