For the most part, there would probably be very little difference in the criminal justice system if state attorneys general were given power over local district attorneys. Therefore, it probably would not matter much in most cases. However, it would matter in some cases. The arguments to be made for each side in this case are similar to the arguments for and against more federal control over states.
The argument for more state control would generally be that more centralization would bring about more even enforcement of the law. If the attorney general had power over the district attorneys, it would be much less likely that a given crime would be prosecuted zealously in one jurisdiction while being largely ignored in another. This would bring more fairness to the system.
However, opponents of this idea would point out that it is better to have more local control. They would say that it is better to let the local district attorneys set priorities since those priorities will be more in line with the desires of their local communities. Therefore, they would argue that less centralization is better.
My own inclination is towards allowing the system to stay as it is, but it would not likely make a huge difference if it were changed.