Deepness and Marooned in Realtime are his favorites of mine. Both sequels to less impressive novels imo. I like his writing in general but those two were really brilliant.
Marooned in Realtime is probably my all time favorite work of science fiction. It altered my perspective on a lot of things.
I love a good murder mystery. And the libertarian/anarchist setting is really fun.
If you haven't already read "The Ungoverned" I recommend it as well - although much shorter it's effectively the second part in a trilogy, bridging the two novels and featuring the same main character as "Marooned in Realtime".