A bit of opinionated, subjective narcissism here, but rank them anyway!

For me, it's settled on:

The Fragile
With Teeth
The Downward Spiral
Broken
Year Zero
Pretty Hate Machine
The Slip

I refrained from putting Ghosts I-IV or the soundtracks in there because the inclusion of vocals and lyrics as primary narrative on an album does make it slightly hard to compare, although I would say that, musically, Ghosts and the soundtracks are the best stuff he's ever written.