Rust in Peace takes the throne here. Probably my favorite metal album of all time.
Technically speaking, I think it has the most well-written music out of all these albums. The guitar work between Mustaine and Marty Friedman, the drumming of the late and great Nick Menza, and Ellefson's basslines are also fantastic. It's the true pinnacle of thrash and it couldn't have had a better lineup.
Follow ups would be AtL, MoP, and RiB.