some cars will run better with different ECU's. Car's that run rich will run better with the leanest chip. Cars with already advanced timing may be prefferential towards ECU's that aren't advanced in timing. In the end, it'll probably be that the best ECU is dependent on the specifics of your car.(i.e. what IC's you have, what turbo's, what fuel injectors and actual flow rates/fuel pressure, base timing, and who knows what else)
