This is so difficult to decide. All these three albums have their qualities. How do they sound, what do I hear, feel and think?
Powerslave is a very balanced and very interesting guitar album. With hardly any effects added, about everything is focused on the playing itself. Naturally this was the case on the first four albums, but here the rhythm guitarists have become individuals experimenting with new styles (they were more one sound on the two previous albums; the first two albums clearly have individual rhythm guitar approach but I'd say it was less interactive). It results in an extra dimension. I love how the tasks are distributed, each with a complementing role (Dave often the fast rhythmic playing, and Adrian the longer chords). A song like The Duellists has the same quality as a song on Moving Pictures: not in style, but the focus on an individual instrument is very rewarding. Naturally, it works excellent as a whole, but listen to a rhythm guitar. listen to that bass.... I can only guess why Nicko allegedly did not like (the recording experience? of) the song. The man had to play the same tempo for 6 minutes. For some drummers it is no chickenshit to play the same all the time; for them it can be more comfortable to deal with rhythm and tempo changes, approaching each segment with a fresh start. Again, this is just my guess. Nicko is not the tightest drummer, and perhaps it was a drama to do all this well (I wish I was a fly on the wall!). But I'm so glad he pulled through. While his drums on this song may not seem that spectacular, I'm still impressed by his playing. Not just because of these probable difficulties. I also like some of his tom breaks and stops (the end of the instrumental section, preceding the main riff), in sync with the others, and the occasional use of china cymbal. Most importantly: together with Steve he laid a perfect ground for Dave and Adrian to play along with Steve's intricate bass patterns. We hear lovely palm muted rhythm guitar, open chords, striking solos and mesmerizing harmonies. Bruce can take a bath, I don't care. What a ride.
I love how the bass, the guitar harmonies, the solos and the drums (such sound and depth!) sound on Somewhere in Time. The balance between Adrian and Dave is uneven. Adrian is the man, not just songwriting wise. In the rhythm guitars he has a libero role at times, doing all kinds of things on the right, overshadowing the softer Dave on the left. Adrian does the most solos, by far, and when you count them up on this album: his very best. Twice as many solos as Dave. Dave does the least amount of solos from his career, but the ones he does (Caught Somewhere in Time, Heaven Can Wait, Loneliness of the Long Distance Runner, Deja-Vu and Alexander the Great) are amazing in sound, ideas and execution, especially the first and last two. The melodies on this album are deeply beautiful (e.g. in the choruses and the calm part of Sea of Madness, the intro of Loneliness or throughout the whole of Deja-Vu). Of course, this album was a game changer. Maiden realized they could add some new sounds and ideas. Although Bruce would have preferred a more radical change with more acoustic songs, Maiden still brought more than just different colours. What about different rhythms? Stranger in a Strange Land and Wasted Years may not be very revolutionary in beat (still executed with lots of feel), the hammering patterns in the chorus of Loneliness and Sea of Madness were entirely new. Especially the one from Loneliness is still echoing in Seventh Son of a Seventh Son, The Unbeliever and several other songs in the catalogue. The staccatoish rhythm in the Sea of Madness verses was a first and last, unique in the catalogue.
Powerslave has its own sound (more of a no nonsense, drier sound than the next albums) and atmosphere, Somewhere in Time has. And Seventh Son of a Seventh Son certainly has as well. The keyboards really open certain channels in the listener (at least in myself!) touching realms unheard of in previous and later records. Somewhere in Time has a very warm, sci-fi sort of vibe. The sound on Seventh Son is a colder, melancholic, sadder sort of sound. The drums sound a bit colder as well, and the rhythm guitars as well I think. Rhythm wise, the sound is a thinner one, leaving room for the keys, Bruce, but also for other nice things in the middle of the audio spectrum. In e.g. Only Good the Die Young there is use of a different guitar sound during the verses. This is examplary of the eerie feel, the mystique this album has. Naturally the acoustic passages contribute to this as well.
So while some ingredients sound less round, less fat, the total of the sound on Seventh Son is a very rich collective, with majestic depth.
Each of these albums have a different approach. Unique among the three, unique among the entire catalogue. Love 'em all.