Reason #6

And finally:
Gandalf defeated a Balrog, he fought the Balrog for 2 days and 2 nights on the peak of Zirak-Zigil
before casting him down to his death until his body destroyed the mountainside. I don't care what you say ,nothing in the HP world begins to compare with a BALROG. Plus: A Balrog is a corrupted Maiar, and it takes huge amount of power to destroy one.

So in the end GANDALF WINS!!!!!!!