The Qur'an is the Greatest Miracle given to the Prophet
The Two Sahihs record that Abu Hurayrah said that the Prophet said,
«مَا مِنْ نَبِيَ مِنَ الْأَنْبِيَاءِ إِلَّا قَدْ أُعْطِيَ مِنَ الآيَاتِ مَا آمَنَ عَلَى مِثْلِهِ الْبَشَرُ، وَإنَّمَا كَانَ الَّذِي أُوتِيتُه وَحْيًا أَوْحَاهُ اللهُ إِلَيَّ فَأَرْجُو أَنْ أَكُونَ أَكْثَرَهُمْ تَابِعًا يَوْمَ الْقِيَامَة»
(Every Prophet was given a miracle, the type of which brings mankind to faith. What I was given is a revelation that Allah sent down to me. Yet, I hope that I will have the most following on the Day of Resurrection.)
This is the wording narrated by Muslim. The Prophet stated that among the Prophets he was given a revelation, meaning, he was especially entrusted with the miraculous Qur'an that challenged mankind to produce something similar to it. As for the rest of the divinely revealed Books, they were not miraculous according to many scholars. Allah knows best. The Prophet was also aided with innumerable signs and indications that testify to the truth of his prophethood and what he was sent with, all thanks and praise is due to Allah.