I had mine on the passenger side of the center console right by the passengers knees, but my next on my next XJ it's going between the visors on the roof. It was hard to hear it on the center console because the speaker was buried on the carpet. I actually had to get an external speaker for it so I could hear it.
I run a full size CB so my mounting option are a bit limited, but other popular choices are the dash by the drivers right knee, console on the drivers side, and in the cubby of the console.