Depends on the enemy.
Vs high def, a % def bypass is better.
Vs low, more atk[depends on the atk too, needs to be something decent as an increase] is better since the % ignored will be like nothing.
Example:
50 def - 5% = 50*0.95 = 47.5 = -2.5 def
20 def - 5% = 20*0.95 = 19 = -1 def