Topic: Degree of Comparison,

Best Answer Explained in Below-:

The phrase "This one is the better-- the two." uses comparative language, where one item is being compared to another. In this context, the correct word to use is "than," which would make the sentence read, "This one is the better than the two." This comparison suggests that one item is superior to the other two, aligning with the typical usage of comparative forms in English.

However, if the intended meaning is to indicate a choice or a segment of a broader category, "of" can fit in phrases like "the best of the two." This expression indicates that among the two options, one is the preferred choice or holds a superior quality.

Thus, the answer is not "of" in this context if we aim to express comparison correctly; it would indeed be "than." This highlights the importance of choosing the right preposition to convey meant differentiation. In this instance, using "than" clarifies the comparative relationship intended between the two subjects being discussed. In summary, "than" is the appropriate choice when establishing a direct comparison.