While I quite like Dream of Mirrors and The Mercenary is ok, they're definitely not on par with some of the classics. And while they don't exactly drag Rock in Rio down either, it's not like they're standout tracks there. Therefore I have to agree about those big 80's live releases having a bit more consistent setlists, as much as I love BNW anyway.
As for my picks... a hard one, again, but for setlist, I'd probably go with Maiden England! LAD/Flight 666 and Rock in Rio have some notable highlights, but some deep cuts like Still Life and The Prisoner, along with Seventh Son gems make the overall representation of my biggest favourites quite extensive.
Performance... well that's Rock in Rio! I do appreciate the fire of the LAD performances and I adore all the post-reunion live records for the very intese executions of the newer stuff, along with some of the best-ever performances of classics stuff like Rime (sorry...) and there's actually a bunch of great performances on Real Ones/Donnington '92 as well, but for me, it's Rock in Rio. The newer stuff, along with Blaze-era picks, sound so fucking intense and the classics selection is executed ferociously! It's a pity they copy-pasted Bruce's vocals though, as it really hurts the dynamic in the choruses of BNW and The Trooper, for example. It would've been interesting if they played Running Free instead of Sanctuary back then... that would've been NOISY!
As for sound... It's much harder choice! I think that Shirley-produced live albums post RIR are actually surprisingly worthy on this department! There's certain level of "dryness" in Flight 666 and En Vivo! but I think they sound fairly good and arguably often give much better representation (soundwise) of the band than some of the more recent studio albums. But I guess LAD takes this cake, in the end. But I'd give a honorable mention to Death on the Road, as it's probably one of the more overlooked live albums on every department.