This question will probably get multiple different responses, because it is a question that the answer is based solely on personal preference. That being said, my favorites are (in no particular order):
Master of puppets
All of the tracks on Kill Em' All are Metallica's best songs in my opinion. :P
Yes Metallica is definatly better U2 although U2 does have some good songs, Metallica has more and the very best songs.
There are 49 songs in Guitar Hero: Metallica.
No there are not Metallica songs in Super Mario 3.....
As long as I know Metallica has recorded 115 songs.
No, never, but Metallica likes Jerry Cantrell
yes you can get the CD of metal militia covering metallica songs
Wikipedia provides information on Metallica and their song 'And Justice For All.' Metallica World also has information about the Metallica band and their songs.
yes
You can play any metallica song with even a 5-piece drumkit. What you need to play Metallica's songs properly is a double bass pedal or double bass drums.
the most common radio channel for metallica played songs in the state of kentucky is 100.1 wkqq
No, you cannot unlock the songs with a cheat.