For me, it's Mindcrime, followed by No Exit and Keeper 2. Justice is one of the only albums where I hold the production against it, and I think SSOASS is way overrated (with the title track and Moonchild being the only songs worth listening to).
This remains, to me, your most jaw-dropping take. If for nothing else, for the mere existence of Infinite Dreams. (But really I think of every song on SSoaSS as at least a 9/10 except for Can I Play With Madness.)
One of these days, someone will have to explain what's so special about Infinite Dreams. The song starts off as a weird effort to merge metal and lounge lizard music. Madness is an awful song. The Evil That Men Do is decent, as is Only the Good Die Young. The Prophecy and The Clairvoyant are boring as snot.
I could make a mirror image statement of my own, where someone would have to explain to me what's so special about pretty much any song on O:M except the two singles and Suite Sister Mary (which I do not like but get why people would).
That Bruce quote Zircon posted is fascinating to me because he's focused entirely on stuff that I think is of secondary importance at best. Could
Seventh Son have told more of a coherent, interesting story if they'd put more time into it? Maybe. But musically it's varied, rich, progressive—a real journey. The title track is a full musical experience in itself. Infinite Dreams, to answer the question, also contains a journey by telling a story with the music. You go from the placid calmness of sleep into the heightening anticipation of the nightmare, to the aggressive intensity of the nightmare itself, to the resolution that the protagonist reaches at the end. I think if you took what Maiden did on
Seventh Son and tried to beef up the "concept" side of it, you'd actually run a real risk of ruining the magic.
Musically, which is what I think matters most, I think
Seventh Son is way more interesting than O:M. And while this is completely a matter of personal preference, I find the story on that album, bare-bones as it is, way more enjoyable than the more fleshed-out O:M story—which I find tasteless and which is an active inducement for me NOT to put in more of an effort to get into the music.
My second choice for this year, since I haven't mentioned that yet, would be AJFA. Depending on the day I might call it Metallica's best album, and it was certainly the most complete one they'd made up to that point.
I should make a point of getting Keeper 2 soon. I like but don't love Keeper 1, but don't have the sequel.