All of the discussion about Cardassians in the philosophy got me wondering what everyone's favorite races are, and if you have a favorite book(s) focusing on them.
For me it's, in no particular order:
Klingons (A Time for War, a Time For Peace, Left Hand of Dstiny, Art of the Impossible)
Cardassians (A Stitch in Time, Terok Nor, DS9 Relaunch)
Romulans (Serpent Among the Ruins, ENT: Relaunch)
In fiction, I really enjoy a good villian, and so I would have to say the Romulans (TOS. TNG. & DS9) because they were always behind the scenes manipulating situations. However, the Dominion would ultimately be my favorite w/ Changeling leaders, Vorta "middlemen," and the Jem'Hadar warriors. The Founders made the Romulans appear tame in comparison especially after the destruction of the Obsidian Order & Tal Shiar fleet & they actually engaged the Federation in a full-scale war.