>Is there any difference between them all, besides the types
>of street crimes that are available?

That's a good question, and I've only completed the Traffic cases, so I can't speak with complete knowledge. I'm assuming the Homicide and Vice will allow for the Free Roam because I was only able to do 10 or so street cases while Free Roaming the Traffic Desk cases. I'm assuming the Homicide and Vice desk street crimes will be similar since I doubt the game will put too much effort in deviating the street crimes and the Traffic desk street cases didn't involve Traffic related crimes at all.

If you can though, check out the secret cars while in Free Roam mode. Some very bugged out designs.