Answer
(Fatwa: 761/761=J)
Muwatta Malik and Muwatta Muhammad do not have same type of Hadiths. Muwatta Malik contains some Hadiths which are not found in Muwatta Muhammad while Muwatta Muhammad consists of some traditions which are not available in Muwatta Malik. The narrator of Muwatta Malik, Yahya bin Yahya Al-masmudi Al-andalusi has collected the traditions and derivations (Ijtehad) of only Imam Malik, while Imam Muhammad has collected the traditions of his other teachers along with Imam Malik. Moreover, Muwatta Muhammad enjoys such characteristics as per Hadith and Fiqh which are missing in Muwatta Malik. Therefore, to me, Muwatta Muhammad is better for studying Hadith and Fiqh.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband