I'd want an album that really has few/no good live recordings. To me Somewhere in Time is the best album that is the least represented live. Somewhere in Time, Stranger in a Stranger Land, The Loneliness of the Long Distance Runner and even Alexander the Great need to be heard live.
Second would probably be the X-Factor. It had a lot of really good songs and I'd like to hear them with Bruce's vocals. Third would be No Prayer for the Dying. Other than Tailgunner and Bring Your Daughter there isn't really any good live recordings from this album. Fates Warning, Run Silent/Run Deep, No Prayer for the Dying and Mother Russia are really good tracks.
Powerslave and Piece of Mind are well represented and there's a really good live recording of the World Piece tour floating around out there. Flash of the Blade is the only Powerslave song I'm interested in...all the other good tracks have good live recordings. I don't care much for the Duelists and I definitely don't want to hear Back in the Village live, ever. As for Piece of Mind, I'm not interested in Quest for Fire and I can live without hearing Sun and Steel live. Other than Invaders there's nothing that hasn't been done live on No# of the Beast, well Gangland, but there aren't many who really want to hear that song live. It's a same Total Eclipse wasn't on the album and Gangland was the B-Side. All the best tracks, except Prodigal Son have been played live from Killers. Charlotte the Harlot and Strange World are the only missing Bruce helmed live songs from the original album, but there is a Charlotte version with Bruce's vocals. Seventh Son has good live recordings. I love the Prophecy but I'm not really dying to hear Only the Good Die Young.
As for Fear of the Dark, only Weekend Warrior and Judas be My Guide interest me. I hate Fear is the Key and Wasting Love, so it would be too torturous to sit through that concert. Virtual XI is the worst Maiden album ever IMO. They would have to completely rework songs, especially the Angel and the Gambler for me to have any interest. I just don't see the love for Futureal either. Other than The Thin Line Between Love and Hate, there's nothing I'm dying to hear live from BNW. They won't play Nomad due to the lawsuit/stolen music used to make that song...but I really don't care for that track anyway.
I think they did all the best songs on Dance of Death Live, except maybe Age of Innocence which I'm probably in the minority for liking. AMOLAD was already performed live in it's entirety and there was a video released. I'd be happy if Maiden just issued a live album of that tour. I thought the Final Frontier was a bit of a letdown in terms of song quality. Other than Starblind there's nothing else I want to hear live that's not already available. Book of Souls would make for a long concert. Shadows of the Valley and Empire of the Clouds would be great to hear live, but I just saw that tour and I don't want to go through all the same songs again.