Five desert island Maiden albums?
The first three are no brainers:
Number
Piece
Powerslave (or maybe Live After Death since it has the four best Powerslave tracks)
SSoaSS is a no go because, although the title track is probably a top-5 Maiden song and Moonchild is really good, the rest of the album is no better than meh.
That leaves two of the following three: self-titled, Killers and Somewhere in Time. Push comes to shove, I'm probably going with the two Di'Anno albums, but maybe I'd swap out Killers for SIT.