The sentence "らいしゅう ちちに 会う よていです" translates to "I have plans to meet my father next week." The verb that best fits in this sentence is "あう" which means "to meet." The other options, "いう" (to say), "かう" (to buy), and "よう" (to do) do not make sense in the given context. Therefore, the correct answer is "あう."