DWI ARREST BUT WAS NOT DRIVING?

My son was arrested for DWI after an officer found him accidentally asleep behind the wheel of his car waiting for a relative to open an apt. complex entrance gate. The officer walked up to the car, found him napping, detected a smell of alcohol and arrested him for DWI. We have an attorney who initially suggested taking it to trial because he was not driving and was on private property. But, now the attorney feels we should accept a plea bargain. Are there any suggestions how best this should be resolved; trial or plea bargain?