Master of Puppets, Ride the lightning, Kill 'em all, And Justice for All, in any order represent Metallica's best work.
Black and Load/Reload are like an entirely different band from the first 4 albums. Black is the best of these, and although not the same band as the "old Metallica", I like it a lot. As someone else said, Load & Reload have several good songs on them, in the same genre as the black album, mixed in with several duds.
I wouldn't wipe my ass with St. Anger.