I fought with this...I wanted to give it to Anthrax cause they don't get enough love and TBH I thought they were the best performance on the Big 4 DVD hands down and the most fun.
Slayer...3 words: Reign In Blood....uggg...so hard.
Metallica on the strength of their first 3 or 4 albums alone.
But in the end I went with
Megadeth...for being the most true to their word and true to their fans without sacrificing growth.
Their overall evolution was the smoothest as well. Alot of Metallica's best music on the first couple albums were penned by Mustaine as well.