I think the fan base as a whole only agrees that the four album span of NPftD through V11 is the worst 4 album span of the band, as to what the best is, I don't think you'll find a consensus.
That's probably true for the most part. I agree that you can ask 10 different Maiden fans what their favorite album is and get 10 different answers. But I think if you asked those same 10 fans for their top five, you'd see some albums that are recurring (POM, PS, SSOASS) and some that may be somebody's favorite, but don't really appear often, comparatively, in the lists of others (SIT, TXF, TFF). So I think we can make some generalizations about what the fan favorites are, though we have to acknowledge that they are generalizations.
For one thing, there is a significant portion of the fanbase that does not really like DoD-TBoS. I don't think you'll find many Iron Maiden fans who don't like TNOTB-PS. And most of the fans like SSOASS as well—only the really anti-synth people don't—and a lot of people put it in their top three. To me, then, it makes sense to call TNOTB, POM, PS and SSOASS the fan favorites.
Since NPFTD-VXI are widely considered to be weak and DoD-TBoS have a significant number of detractors (seriously, look at how people who love Iron Maiden's "classics" often feel about those albums. You can find them in reviews of those albums or in comment sections on articles posting setlists from the AMOLAD or TFF tours), that leaves IM,
Killers, SIT and BNW unaccounted for. I chose
Killers because a lot of the NWOBHM or thrash metalhead people really love that one (look at what happens when they talk Iron Maiden on That Metal Show, for example—Trunk and his crew go straight to
Killers), and BNW, because that got a lot of goodwill for being the "return" of Iron Maiden. But I could see an argument for IM or SIT.
And again, this is all guesswork. But I think there's some validity to it.