Best Metallica album ??

Its nearly impossible for me to pick the best Metallica album. I went with Puppets but the first 4 are all so good. Now Megadeth on the other hand would be Rust in Piece hands down. Also, The best Slayer album would be Reign in Blood, Best Anthrax would be P.O.T., Best Testament would be Low and the best Sepultura would be Chaos A.D.