Does he make a good witness? How strong is the judge? What is the prosecutor's track record? Are you a compelling witness or not?
You leave must unanswered.
There is a lot more information needed before a "strong" opinion can be provided. As for criminal records the DA is correct. If you testify and you have certain convictions for deception, fraud or false statements then you can be impeached. This is also true for the Defendant, but he has no obligation to testify and so his convictions would not be presented to the jury.
Finally, my colleagues are correct that the case is in the hands of the prosecutor and you are the victim/ witness. You have certain rights as the victim, but ultimately the decisions on how to proceed is in the hands of the prosecutor.