Here's how I'd rank them:
1) Rust In Peace
Easily their best work.
2) Countdown To Extinction
I can play this album straight through and enjoy it. Nice flow. One of my favorite albums that I grew up with.
3) Peace Sells..But Who's Buying?
Quality stuff here. Could easily be their second best album, but I put Countdown at #2 for personal preferrence.
4) Youthanasia
If you bought the cassette of Youthanasia then Side 1 is what you'd want to listen to; from Reckoning Day to Elysian Fields. I like the overall sound of this album.
5) Cryptic Writings
Like Youthanasia, the first few tracks are pretty good. Trust, Almost Honest and Use The Man were a good way to start off the album. Listening to this you can really tell that Dave was trying to write songs that were less heavy and more for radio airplay.
6) So Far, So Good..So What?
A few memorable tracks (In My Darkest Hour, Anarchy In The UK cover).
7) The System Has Failed
#7 and #8 could really be interchangeable to me. I like the albums but for some reason they just don't jump out at me.
8) The World Needs A Hero
See #7
9) Killing Is My Business...And Business Is Good
Doesn't really do anything for me.
10) Risk
The "experimental" album. Some friends of mine have said that this was Dave's response to Metallica changing their style with Load and Re-Load. Either way, it's a miss.
Excluding: Hidden Treasures, Capitol Punishment, Rude Awakening, Still Alive...And Well?, and Greatest Hits
EDIT: I used the original recordings as my basis, not the remastered ones. It's nice that they included some demos and whatnot, but I didn't care for the remastering.