1. The Fragile-Not only is this album epic, but it contains an example of all the different musical styles of NIN, making it the one album that can give any listener the true definition of NIN's sound.
2. The Downward Spiral-Not much to say that hasn't been said already. I think the Fragile and this album tie as NIN's masterpiece.
3. Pretty Hate Machine-This was my favorite up until the Fragile was released. I've always been big on electronic music and the 80s sound. I probably play this one the most out of the entire catalog.
4. Ghosts I-IV-I always wished for NIN to do soundtracks and this was sort of the first taste of that. The Social Network and Girl With The Dragon Tattoo (two of Trent's best work IMO) evolved from this stuff.
5. Year Zero-A really cool concept and some great songs. It does get a bit draggy, but it is a very unique album.
5. With Teeth-This sort of sounds like a "cliff notes" version of the Fragile, or even a more radio friendly version. It doesn't offer anything new to the catalog, but does contain some of his best songs.
6. Broken-I like metal, but I'm not a huge fan. While this album is awesome, I prefer more diversity in an album, I suppose that is why it is shorter than the others.
7. The Slip-Very enjoyable, but like With Teeth before it, it doesn't offer anything new to the table. It has a lot of good stuff, but it sounds more like a collection of outtakes from Ghosts, Year Zero and With Teeth.

I don't consider Still to be an actual album, as it contains re-workings and material meant for the movie "One Hour Photo".