I havent heard all maidens, but most.
I personaly would only bother partly with seventh son, and pay very much attention to number of the beast, powerslave and brave new world.
everything from their debut album up to Seventh Son.. my personal favorite happens to be Live After Death even though it's a live album.. I just thought they were better live then on studio albums..
Seventh Son has been my long time favourite, although I don't think it's any better than Powerslave, Somewhere In Time, Piece of Mind, The Number of the Beast, or indeed a lot of their earlier material.
I like Powerslave and Somewhere In Time just as much, and I would never be without The Number of the Beast.