Note: operas are in random order, the first I analyze is not necessarily the best.
[ I ] - Renata Tebaldi, Carlo Bergonzi, Giulietta Simionato, Wiener Philharmoniker (Herbert von Karajan), 1959 Even if it's a little old, its without audience, the sound quality is good, singers are top-notch, plus they're Italians, so they pronounce well, orchestral parts border perfection.
Just listening to the Prelude puts you in a good mood: the dinamic is maybe a little exaggerate (blame the sound engineer or it's just the orchestra that plays too well?), but the effect is passionate and captivating; also the celebrated March and the dance music (Ballabile) are remarkably well played.
If you want an Aida for a first time listening, then go for it. In my opinion, it becomes a little boring after a few times, but can't still figure out while.
[ II ] - Maria Callas, Richard Tucker, Fedora Barbieri, Tito Gobbi,
Orchestra e Coro del Teatro alla Scala di Milano (Tullio Serafin), 1955 If you like Callas, then this is one to buy. No audience ( = no screaming), great cast - even if I can hardly bear Tucker's speaking: that's definitely not italian, maybe an alien from Mars would speak better... but it's like Corelli's little pronunciation fault: after a while you get used to it and hear only his beautiful singing.
On the sound quality side, we are on a slightly lower level than that of the former (it was also recorded four years early): strings lack of body and brasses sound a little distorted... which is terrible considering how much Verdi, particularly in Aida, relies on their strength.
The orchestra is still very good - but the March is rather out of tune - and the choir is somewhat less unite and quite sloppy - but they don't seem the same choir that recorded Macbeth in 1952, same place, different conductor, harder music.
[ III ] - Maria Callas, Mario Del Monaco, Città del Messico, 1951 This is for radicals. People with sensible ears, don't buy this... sound quality is just awful, closed, distorted, deformed in the forte, noisy and even recording speed isn't uniform.
We haven't yet finished: it's live and so it's covered with cheerings - but it's something like an historical document, and features a wonderful Callas' E flat six seconds and a half long!
[ IV ] - Nilsson, Corelli, Bumbry, Sereni, Orchestra e Coro del Teatro dell'Opera di Roma (Zubin Metha), 1967 Well, the orchestra really seems hieratic here (in a good meaning), but when it's time, it unleashes all the sound and the pathos needed - in absolute self-control.
It's superfluous to talk about Corelli. His legato is unparalleled and only a couple of acutos seem a little less than fluent - the remaining notes he sings are easy and natural, like he's making no effort at all. That's the way it should be. Oh, not to forget some thrilling pianissimo, e.g. at the end of his first aria ("Celeste Aida" - "Heavenly Aida", as everyone knows), when he says "vicino al sol" - "near the sun", started forte and then ended pianissimo (and held).
I know that it's not written like that: just try to start an acute B flat pianissimo and see if you can. Del Monaco in Mexico City starts and ends fortissimo, neither Tucker does the diminuendo: only Bergonzi attempts something like a mezzoforte, pretty successfully, I must say.
I know there is an Aida with Domingo, Caballé, Cossotto, Cappuccilli and Ghiaurov, 1974 studio recording, but I never had the pleasure to listen to it. Moreover, it's directed by Riccardo Muti, and I don't like him very much...
Other I know of and may be worth a try is Dimitrova, Pavarotti, Nucci - Maazel. I also know that there is a live recording made in Teatro San Carlo of Naples, with Corelli and a monstrously wonderful Fedora Barbieri, conducted by Vittorio Gui, but I don't know if it's in stores. When I overheard it (alas, just until "Quale insolita gioia" - "What sudden joy"), I noticed that sound quality was really bad, seemed like microphones were set towards the audience and everyone was suffering from pneumonia... fortunately things get better after the first part of the Prelude...
Bottom note: avoid like plague cheap editions. I bought two other Aidas (which I don't mention), and listened to them once. Stop.