There is no definitive answer to the question of Allah's favorite number in Islam. The concept of Allah having a "favorite" number is not explicitly mentioned in the Quran or Hadith.
While some Muslims associate the number 786 with blessings due to its numerical significance in representing the phrase "Bismillah al-Rahman al-Rahim" (In the name of God, the Most Gracious, the Most Merciful) in Arabic numerology (Abjad), this is more of a cultural practice than a theological belief. The Arabic letters of this phrase, when assigned numerical values, add up to 786.
It's important to remember that assigning specific numbers as "favorites" of Allah is not a core tenet of Islamic faith. Devotion and good deeds are valued more than the association with specific numbers.