*I review both 1.0 and 2.0 here, and frequently compare the two.
*I'm going to assume you've seen the movies they're from, so there will be slight spoilers if you haven't seen them.
Okay. Let me start off with a little background about my experience with soundtracks. I've owned TONS--from Howard Shore (Lord of the Rings) to John Williams (Star Wars); from Toshiro Masuda (Naruto) to Nobuo Uematsu (Final Fantasy); from Akira Ifukube (Godzilla) to Jun Senoue, T. Ohtani and gang (Sonic Adventure 2). All of them have had their diamonds, along with the coals. Up until I bought these two tracks (Evangelion 1.0 and 2.0), the long-time reigning king was Nobuo Uematsu. Well, ladies and gentlemen, I'm here to tell you he's been dethroned. There's a new king in town: Shiro Sagisu.
*Regarding 1.0:
This track is shorter than the first, but that doesn't necessarily make it worse. In comparison to 2.0, it definitely has more mellow, piano-oriented tracks ("Rei-Opus" IV and V; "Cruel Dilemme" I, II, and III; "Crepuscule - Tokyo III"; among others). If you HAVE to pick between one or the other and like these kind of tracks, this may be your clue as to which one to get (it's also cheaper). However, it still, of course, has its share of epics ("L'Attaque des Anges" and, the champion, "Angel of Doom").
*Regarding 2.0:
This is definitely my personal favorite between the two. Some of my favorites include: "Destiny," "In My Spirit," "At The Very Begining," "Kyou no Hi wa Sayounara," "Les Betes" (not to be confused with the track with the same name from 1.0; the version in this album is basically what happens when you put that one on steroids). But my all-time favorite is the song during the ending scene: "Tsubasa wo Kudasai" ("Please Give Me Wings").
Which brings me to a few issues some people have brought up. Some people have said that two songs don't fit their scenes very well, claiming them to be soundtrack dissonance. The first is "Tsubasa wo Kudasai," which plays during the ending scene. This song, I say, fits the scene perfectly. In all of my experiences with soundtracks, I honestly couldn't think of a song more beautiful/fitting for the scene. The other is the song that plays when Unit 03 (with Asuka inside) is being eviscerated--"Kyou no Hi wa Sayounara" ("Today is the time for goodbye"). This one, however, I believe did not fit the scene too well. A sadder, more depressing piece should've been used. And the fact that the time between these two instances of soundtrack dissonance is so short does not lend well to their cases.
The other issue is that there are duplicate tracks. This, simply stated, is false. In most of these cases of duplicity, one track is actually a demo version (AKA unfinished version) of the final cut. It's interesting to see how one song changed from said demo to the final product. Also, there are two versions of the songs "Tsubasa wo Kudasai" and "Kyou no Hi wa Sayounara." The first versions are the normal versions you hear in the movie. The second versions are tributes to "Sound of Music." One is not more or less complete than the other--the tribute versions are just very interesting versions that are different without radically altering the original.
*Together:
It's amazing to go back and see the difference between now and back during Neon Genesis Evangelion. Some of the tracks you'll recognize and say "HEY! I know this song!" Although now, they're better than ever (undoubtedly thanks to improvements in Shiro Sagisu's skill as a composer, as well as a vastly improved budget).
Between these two tracks, I've had dozens--if not over a hundred--hours of replay value. The songs are deep, inspiring, uplifting, touching. (Personal recommendation: Pay special attention to the lyrics of "Tsubasa wo Kudasai." It's one of the most beautiful songs you'll ever hear.)