What is a student of Islamic knowledge advised to begin memorizing from the authentic Hadith books: An-Nawawi's Forty Hadith, Al-Maqasid al-Hasanah, or Kashf al-Khafa'?

Al-Maqasid al-Hasana by Al-Sakhawi is a useful book, but it is not for authentic or well-established hadiths. Rather, it is for hadiths that are widely circulated among people, which may be unestablished or fabricated. Therefore, it is not advisable for a beginner to memorize it. We recommend memorizing Al-Arba'in an-Nawawiyya, then Umdat al-Ahkam, then Bulugh al-Maram, and then the two Sahihs.