I think i'll side with Thanos in a VERY close battle, he's been able to attack the minds of the Fallen One, he's has enough power to put Galactus on his butt and his intelligence are a great factor in this one, not to mention his durability. But MM has a chance to win, if he can speed rush alot then maybe it would keep Thanos off balance to execute cosmic attacks., still siding with Thanos though.