Joe,
I've seen some pretty peculiar polls posted by you lately and this one takes the cake. Although this poll far more interests me than finding out who on a forum about pornography is still a virgin, it is impossible to compare Iron Maiden and Metallica. They are simply the best two heavy metal bands of all time but their music is so different from each other.
This is a tough one but I'm gonna have to go with Maiden. There are many reasons for this choice but all you have to do is listen to Metallica's last two CDs. Absolute junk, they should have never sobered up. But what it really boils down to is I can still pop "Number of the Beast" into my CD player and I get the same buzz I did when I first heard it 22 years ago (omg!).
Maiden's got a very "heavy", complex, and actually somewhat melodic sound whereas for sheer power and aggression you cannot beat Metallica's first 3 albums (and Master of Puppets is an absolute masterpiece of power metal).
But to me, Maiden has stood the test of time quite a bit better, so I'm going with Eddie and the gang.
Great poll though, Joe.