Master of Puppets. It's their most consistent, has their absolute best songs, the best production and Hetfield had matured into a pretty good vocalist on the album.
...and justice for all has the best songs and lyrics, has the most developed voices but is not very consistant. i have to skip some songs, on KEA and MOP i dont
so im pretty in the middle of all three. plus the production was a lot better on MOP and AJFA. KEM, RTL, and all others the prod sucked donkey dick.