Black Album was the peak of their popularity and musicality IMO.
That said, Kill Em All is still my favorite, when they were young and hungry. Not to mention Cliff bad person Burton.
In the 90s, I knew a singer who would write out all the lyrics on big sheets of poster board with a sharpie. He had a thick stack of gigantic cue cards that he would lay on the stage in front of himself and fumble with between songs. It was embarrassing to watch.