Not sure about the accuracy part, in both T2 and T3 , The t800 fired off entire belt fed magazines with a minigun at large groups of police officers, and did so without injuring a single person. Pretty insane. But those parts were easy to forget and Robocops accuracy was definitely portrayed better imo.
Accuracy with a minigun is better, but Im probably siding with Robo as well, im assuming same weapons. If you gave both of them a rifle, no doubt in my mind they would both clear probably any range you set before them, but Robocops portrayal of his accuracy was better imo. And if anyone has ever played the robo app game ( not that that is relevant here) accuracy is the main thing.