I hope it's Ok that I say my two cents here on the forum after a long time not writing at all. I do however read the topics quite often...
Maiden is by far the biggest band in the world, if the opinion is coming from musicians and fans. If you take the side of promoters and record labels or retarded Rolling Stone magazine American editors, then for sure Metallica.
Iron Maiden continues to be a niche type of music and Metallica is pop metal/rock. They have been doing this pop/metal formula with heavy guitars and Winnie vocals for 20+ years....
Their last album has one metal song, the rest is just a bunch of heavy sounding songs with pop vocals on top....I hate the black album, since it came out, I could never get into it. It's like I could feel there was something really fake about it...
Anyway, Maiden reigns as the true metal legends in the eyes of the true metal warriors of this world!