To me its not clear. Over the course of playing this game I have tended to play Nickel vs the Shotgun instead of playing Dime. To me, its too difficult to have that much depth at DB.
With the 3.0 engine, you you do have a little more flexibility in defensive planning. You can set up a Dime so that it acts more like a Nickel, or even a 4-3. You can set up a 3-4 so that it looks more like a Dime.
So, in short, I suggest trying out what you think is best, based on your personnel, and settling on what gives you the best results.