All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
It was narrated on the authority of Al-Baraa’ ibn ‘Aazib that he said: "The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, had the most beautiful face of all people and the best conduct. He was neither very tall nor short.” [Al-Bukhari and Muslim]
However, we do not know any evidence proving who the most beautiful woman was. Additionally, knowing this piece of information is not beneficial and not knowing it is not harmful. A Muslim should ask about things requiring actions which are beneficial to him in his religion or his life.
Allaah Knows best.