Your answer would be A, Spring A has more potential energy.
Potential energy is exactly what it sounds like - energy that has the potential to exist due to stressors, but doesn't yet. In this case, the spring is ready to jump back into its original position however it can't because of it still being stretched, therefore this tension is what creates potential energy.
When you measure potential energy, the one with greater of it is the one where it has more stress being placed on it. In this case, spring A is being stretched furthest so it has the most potential energy.
Hope this helped!