It would be too easy to say Live After Death.. but it is good for sure.
I find myself liking Iron Maiden more and more, not that I disliked them to begin with but I was certainly a late starter. I preferred Motorhead, Judas Priest, Sabbath and so on at the beginning.
I don't think they've written an album that didn't have a track or two of filler on it though, theres no perfect Maiden album.
* Iron Maiden - has a rough and ready feeling going on and fun well written songs. Certainly one of my favourites.
* Killers - there are a few good tracks, but in my opinion alot of filler too
* Number of The Beast - would be a good starting point, its mostly all excellent. it might eb the peak of the NWOBHM
* Piece of Mind - this is a good album for sure, it has kind of a power metal feeling. The first half until Still Life is all very good
* Powerslave - Like it alot, theres some staples here. But again, some lame tracks (Back in The Village etc). Its a must listen for Rime of the Ancient Mariner, Aces High, the title track etc
* Somewhere in Time - I didn't like this record for years, but I'm warming to it more and more. I tend to cherry pick my way through it.
* Seventh Son of a Seventh Son - all top quality stuff. Probably not right as an introduction to the band, but its really fine to listen to it end to end
Then I would say, except for the odd track (Holy Smoke, Fear of the Dark) its all pretty dire until
* Brave New World - a welcome return to form, really like this album
* Dance of Death - The second Maiden studio album I listened to. I really got into it and think its one of their best
A Matter of Life and Death/The Final Frontier are all very progressive. Its a different sound they've gone for. I find it a bit overblown/boring, but can imagine some prefer this sound. Again theres a few killer tracks in this period. I like El Dorado for example. Its a million times better than their 1990s stuff for sure..