I am an avid fan of the CSI series and buy all of the boxsets. I have to say my preference is certainly vegas as the characters are fantastic and all storylines intriguing and different.  CSI New York and Miami are also good to watch.  So far my favourite episode is the Quentin Tarantino season finale called Grave Danger which is a two part episode, it was absolutely fantastic and even now into the 8th season of CSI they are still coming up with new ideas to keep the viewers in suspense and glued to their TV sets.