That is a really tough choice cuz they ruled in the 80s. I voted Master Of Puppets. I also love Ride The Lightening and Justice for All, and even Kill Em All...they were all very influential albums for me.
Yeah, they're all fantastic albums! I actually still love Metallica, and even though I do think their last two studio albums are not nearly as good as their first four albums, I do like most of the songs on them. I rate Metallica's studio albums like this:
I voted Master of Puppets,although I cannot be completely sure I would not like ..And Justice for all more,as I do not own it.Although I get the impression I would not from reviews I have read.