A good question having no set answer. These terms are ambiguous and highly subjective. On the same day they may have wildly different interpretations depending on the venue, the makeup of the jury, the politics of the day, or any other variable. Not to mention that reasonableness and prudence may be at odds with each other in a given circumstance.
For instance, it is perfectly reasonable for a convenience store to charge inflated prices for basic food items compared to a grocery store, making it prudent for a consumer to shop at the grocery store. However, if the consumer has an immediate need for milk at home and the convenience store is the only place open, then it would be prudent to buy the milk there rather than wait for the grocery to open, or even to drive a significantly greater distance to a grocery.
More importantly, what matters is what the judge/jury thinks, or can be convinced to think, that matters at trial. You might even say that it is the defendant’s own beliefs about what is reasonable and prudent which are on trial since it can be argued that those beliefs are what led to the actions in question.
Clear as mud, right?