Having gone through a pretty intense Maiden period a couple months ago, the reunion albums are pretty fresh. I know for me, for a long time I thought that - except for AMOLAD - each subsequent album was better than the one before. Now, for me, it seems that the best one is the one I listened to most recently. I got En Vivo! last weekend and went back to refresh on TFF studio tracks, and man, I love that album. It's not as dense as AMOLAD, but with more substance and intricacy than BNW.
It changes from moment to moment, but this is where I am now:
The Final Frontier
Dance Of Death
Book Of Souls
AMOLAD
Brave New World
That's a relative order though; it took a long time, but seeing "For the Greater Good of God" live, then relistening a couple times over the past couple months, AMOLAD really clicked. So being fourth on THAT list, isn't a bad think at all. The only album I don't go to much is BNW.