Which word best completes the sentence: The person __________ made these delicious sweet tarts has my vote.

The correct word to complete the sentence is "who." This term is typically used to refer to the subject of a verb in a clause, making it appropriate for this context. In the provided sentence, "who" introduces a relative clause that describes "the person" as the subject who made the sweet tarts. This usage allows for clarity and connection between the subject (the person) and the action (made the tarts).

While "that" can also be used in similar contexts, it tends to refer to things or objects rather than people, though it is sometimes informally used for people as well. "Whom" is generally reserved for the object of a verb or preposition, which does not fit the grammatical structure here, and "whose" indicates possession, which does not pertain to the action of making the tarts. Therefore, "who" is the most suitable choice to complete the sentence accurately.