Probably easiest to pick a favorite song by category since it's so tough to just choose one song, but I'll try anyhow.
Since my favorite band is Metallica, it must be one of their songs. All of them deserve #1 to me, but the very slight lead goes to
Battery. It's fast, aggressive, and opens up one of their best CDs.
*after listening to Master of Puppets again today, I want to make
Sanitarium tied with Battery for 1st, since it's kickass