Final answer:
The most correct sentence to use is: 'Which ballpark has the deepest outfield-Fenway Park or Yankee Stadium?' Using the superlative form 'deepest' is appropriate when comparing two things and indicating that one has the most extreme characteristic.
Step-by-step explanation:
The most correct sentence to use in this case is: Which ballpark has the deepest outfield-Fenway Park or Yankee Stadium?
In this sentence, the superlative form 'deepest' is used to compare the outfield of Fenway Park and Yankee Stadium. When comparing two things and indicating that one has the most extreme characteristic, we use the superlative form. In this case, we are comparing the outfield of two ballparks to determine which one is the deepest.
Using the superlative 'deepest' emphasizes that one ballpark has a more significant depth in the outfield compared to the other.