My favourite has always been CSI: Las Vegas. I loved Grissom's character. Now that he's gone, I just haven't been able to watch the show in the same way. Cases are less interesting and Grissom was a huge driving character. I don't mind NY, but can't really stand Miami.
I have to say CSI: Crime Scene Investigation aka: Las Vegas. It's always been my favorite. I don't like Miami at all. I've only watched one episode that I've liked, and that's because Michael Shanks was in it. I just don't get the David Caruso factor. I do like NY and Gary Sinese, but for some weird reason, it didn't really hook me. I watch it occasionally but not regularly.