I'm sick and tired of people constantly arguing over which of the two, Metallica or Megadeth, is better than the other. No matter what anyone says, writes, or does, nothing will change the fact that whichever side you choose is purely a matter of opinion. Therefore, neither of the two bands can be proven better than the other. So stop fighting over it!
Now, I personally favor Metallica. But like I said, that's my opinion. If you like Megadeth more, then that's your opinion, just keep it out of my face.
Bottom line is; you will never be able to prove on band superior to the other without somehow invalidating your claim with your own personal opinion.