Does supplicating with "Allahumma" entail supplicating to Allah by seventy of His Most Beautiful Names, and has a Prophetic Hadith been reported confirming that? And what are the best formulas for supplication: "Allahumma," "Ya Rabb," or "Ya Allah"?

"Allahumma" means "O Allah." The 'mim' (م) in it is either a substitute for the vocative particle 'ya' (يا), or it was added for emphasis, or to indicate collectivity, as if it means "O You to whom all the Beautiful Names belong." As for the idea that its meaning is to supplicate with seventy of Allah's Beautiful Names, this is a statement attributed to Abu Raja' al-Utaridi, but it requires evidence. This supplication has been frequently used in the Qur'an and Sunnah. Al-Hasan al-Basri said about it: "Allahumma is the compilation of supplications." And Al-Nadr ibn Shumayl said: "Whoever says: 'Allahumma' has supplicated to Allah with all His Names." No evidence has been reported regarding a preference between supplicating with "Allahumma" or "Ya Rabb" (O Lord) or "Ya Allah" (O Allah).