It's hard for me to answer that, since I tend to rate bands as a whole, rather then individual records, so for me the question itself is somewhat incorrect. That being said, I'm current rocking the first two CDs of the box set, since they are live, and both give a really good cross section of the band over the years, and Imperial Wax Solvent, if nothing else then for "Exploding Chimney"
However, I have noticed that the live ones tend to hold my interest more then anything else, which is weird for me. I think it's along the lines of how The Pine Box Boys, or GG Allen are; You just don't get the whole picture when Smith has been put through the industrial processor.
It's also kind of difficult to figure out where to listen to them. Sometimes cruising low and slow in my car, sometimes blasting down the highway in a HMMVW with my gear on, pretty much never when I'm working out.
This tour out (starting tomorrow), I'll be listening to the "Extricate" album, so I'll see how that goes.