My fav? "In Conquest Borne" by C.S. Friedman, and by a very large margin. The only flaw is that you can easily guess who's going to "win" in the end (but not how).
I've tried reading that one but never could get through it. I have read the fantasy trilogy. Still prefer Asimov over it I have to admit.
Now that I think about it, I may be a little prejudiced. My best friend at the time just flat
was Harkonnen, and I got a real kick out of finding such a perfect description of him in fiction.
But I still have to say the ICB universe was well conceived, and in extreme detail. It's a little tricky to read since some of the chapers are almost totally independent short stories. My favorite of these is about the Harkonnen youth who's trying to assassinate his old man.( I also know someone who was kinda like the old man if you exaggerate him a little.)