Here are some other categories where Megadeth and Metallica are contenders for the top spot. And the awards go to:
Biggest Crybaby: Dave Mustaine
Biggest asshole: tie between Dave Mustaine and Lars Ulrich
Most anti-consumer: Metallica
Best lineup in the history of thrash: 90's Megadeth (Mustaine, Ellefson, Friedman, Menza)
Biggest difference between their best and worst music: Metallica. I think it's inarguable that Metallica has made the worst songs in the history of thrash. Although you could say a whole lot of it is not thrash at all. Then they have three albums that are absolutely excellent.