AMOLAD without much thought. It is the pinnacle of modern Maiden and my second favorite after Piece of Mind.
After that I think I have to go with TFF. It has some issues and it hasn't aged as well as some of the others, but I really like how adventurous some of the songs were. It also feels like the most varied Maiden reunion album. The other ones stick pretty closely to one sound, but TFF really jumps around. I also like how the epics are all together. It reminds me of a traditional double album, where one disc is a certain flavor and the second disc is another flavor. In vinyl terms it is a double album (as are all their reunion albums save for TBOS which is a triple) though it wouldn't be divided evenly with the shorter songs on one disc and the epics on the other, but I digress. Once the final crash cymbal hit of The Alchemist fades out and the wind sounds of Isle of Avalon fade in it's like the start of an entirely different album. It's awesome. I still remember hearing it for the first time, it's like we were getting two Iron Maiden albums on the same day.
The Book of Souls comes next. Also ambitious, being a double album and having some of their longest songs. Also surprisingly not bloated. I think the album would be better without Shadows of the Valley but other than that it's excellent. Over a year later and it still kicks ass.
Brave New World is an excellent return to form for them. Its low ranking speaks more to the quality of their reunion work than it does the quality of the album, as I consider it a modern Metal classic at this point. It has the energy of 80s Maiden but they're clearly progressing. They didn't throw the development during the Blaze years out the window, instead they developed on them with the new lineup. This is key to their longevity IMO.
Dance of Death is at the bottom, but it's still a good and necessary album. A lot of the experimentation on this album had varying levels of success, but it led to some of their best work on the following albums. Once again showing what makes Maiden so great: Instead of taking the safe route and doing BNW again, they decided to take some chances. They did an unplugged song, they tried a modern story-based epic, they even had Bruce rap in the bridge of a song. It's uneven and pretty ugly sounding, but it has its place in the band's history and is one of their most important albums in terms of development. It also has Paschendale which is among their best songs.