Number of the Beast was first, but it was not long after Piece of Mind had already came out, so that was my second. All of course on cassette.
After a while tho I sort of fell out of the metal scene, which I think was sometime mid 1993. Was definitely after Metallica toured Aus for the Damaged Justice tour, and then the black album came out, which felt like a bit of a letdown, so that was probably the start of when I fell out of the scene (even tho around that time Fear of the Dark came out, which I had). I was in my mid-20's at this stage, and work wasn't a very metal-friendly place. :/
Then I had most of my CD's and tapes stolen from someones car, which didn't help.
And then about 8 yrs ago fell back into it. Mainly thanks to BangerFilms `Metal: A Headbangers Journey`, quickly followed up by `Metal Evolution` (remember seeing that in mid-2012), which suddenly dragged everything full circle cos of the use of The Trooper as the intro music. So once again I was hooked on Maiden (and metal in general).
So your another old fart!
Out of the universe, a strange light is born
Unholy union, trinity reformed....