You get points for crossing a defense the second time, just not the third. So it really is just a matter of which undamaged defense is most convenient to cross.
Also, just to clarify terminology, because it is actually very important to understanding the rules:
- A defense that has not yet been crossed is an undamaged defense with 2 Strength
- A defense that has been crossed once is an undamaged defense with 1 Strength
- A defense that has been crossed twice or more is a damaged defense
- A breach occurs when 4 of the 5 defenses have been damaged