Disc 1.
The second disc is amazing, but still feels like the second half of something. If you got rid of disc two, god forbid, disc one would still sound like a complete album.
Exactly. Disc 1 has If Eternity Should Fail (the opener), Speed of Light (the quick one), The Great Unknown (the weird one), The Red and the Black (the epic), When the River Runs Deep (the melodic, kind-of-filler one) and The Book of Souls (the title one). And IESF, TGU, WTRRD and TBOS are incredible.
Disc 2 has Shadows of the Valley and Empire of the Clouds.