[Ali Imran]

It took you very long to say that this belief about Jibril is an assumption.

Now as to which angelic being is the mightiest, is there a Qur'anic verse to support your assumption that it's Jibril and not Michael or Satan?

The message of the Quran cannot be from satan using the criteria given by Jesus in the book of Mark. Can we clear that one first? Once we are clear that it cannot be from satan, then we can go to the next step. Who else could have brought such a message.