The Sound of Perseverance, without a doubt. I think it's the most progressive of them all. The playing is highly technical as usual, but on this album there's a little more room for experimentation and soloing from each member of the band, due to the structure of the songs, which is more "loose". Well, Schuldiner has never exactly stuck to classic verse/chorus/solo/chorus structures, but this time the pieces are lengthier and there are more radical shifts of passages during every track. I think that previous albums suffered from an occasional "stiffness" and lack of balance (technicality slightly overweighed composition at times), whereas on TSoP the balance is just right, showcasing a more mature approach to songwriting. As a result, there's also a lot of emotion emanating from the harmonies and melodies throughout the album; the lyrics are also better crafted and the music is touching in many ways, which is not exactly a common thing with death metal albums.
All albums from
Human onward are outstanding. But, overall, I think this is their finest, similar to none other, holding a special kind of beauty, and definitely one of the most progressive releases of the tenth decade.