Just noticed I haven't done this before. I think you could actually take both albums and make the reunion era's greatest album by far, although the albums are pretty different from each other. What it comes down to for me is that 75% of The Final Frontier is GOAT Maiden, but it has a couple clunkers. Book of Souls is a consistent listen, but very rarely reaches the stratosphere. So if you replace the Final Frontier fillers with Book of Souls classics, you've got a pretty excellent album.
I gave myself a couple of additional challenges:
1 - No double album.
2 - It has to follow the general "rules" for Maiden. In other words, The Talisman and The Book of Souls can't both be on there, only one acoustic Janick epic. Killing The Talisman was brutal, but The Book of Souls might be the best song in the reunion era.
1: If Eternity Should Fail
2: El Dorado
3: Mother of Mercy
4: Coming Home
5: The Alchemist
6: Isle of Avalon
7: Starblind
8: The Book of Souls
9: The Man of Sorrows (yes, really)
10: When the Wild Wind Blows